Hi everyone. I am a bit of a hobbyist but haven't done any electronics work in a while and am new to this forum. I am currently working on a project for fun. The basic idea of what I want the circuit to do is this:


Main Function of Circuit:
----------------------------
1) User switches power on to circuit.
2) Piezo siren triggers every few seconds for .5 seconds or so
3) User adjusts potentiometer to set a time limit from 30 to 60 seconds.
4) User presses a button which starts the first 555 timer as a monostable oscillator and stops the piezo siren from going off.
5) After the first 555 timer sequence is complete, the second 555 timer is triggered as an astable oscillator to start, this powers a piezo siren every couple of seconds for a .5 second interval or so.
6) User turns off power to circuit and siren doesn't play anymore.

Other Functions:
---------------------
1) User can switch an LED off and on while the power is on to the circuit.

I had all 6 steps working perfectly on a breadboard and moved on to soldering everything onto a PCB board, but that is where my troubles started.


The Process I have gone through so far:
--------------------------------------------
After soldering everything onto the board (including the CR2032 battery holder), the LED and the rest of the circuit did not turn on, so I removed the batteries. I used a very small flathead screwdriver to make sure the areas between different solders were clear of any possible trace lines and tried powering on again for a short time, but no luck. Since then, I used a dremel tool to REALLY make sure none of my solder connections were touching, then cleaned the bottom of the board with rubbing alcohol and a toothbrush. After letting it dry for a while, I tried a final time but to no avail.

I have re-drawn the schematic (painstakingly) from the actual finished soldered circuit and checked it against the original I drew up that worked in the breadboard, but haven't been able to find any differences. At this point, I am thinking that I may have blown something due to a short resulting from a bad solder touching something it shouldn't have. With all of the components soldered in, taking them all out and replacing them with new ones would take forever, and if that isn't the problem then I'm still stuck and now just out more $. Nothing looks visibly damaged but I am not sure if any of them would show visible signs if they were burned out. The other alternative is that my original circuit was bad and perhaps I overloaded the transistors or 555s.

I have attached the schematic I re-drew from the actual soldered board as is, along with pictures of the actual circuit. The siren came with a built in driver circuit which I have removed from its original enclosure and placed on a separate breadboard from the main board. All transistors are NPN. At this point, I am 99% certain that the circuit is exactly as shown in my schematic that I am attached and does not have anymore soldering issues, which leaves either fried components or a bad original circuit to blame. Right now, when I do a check of resistance from power to ground with both of my switches open and without the battery attached, I get a resistance of .3 to .5 Ohms which doesn't seem right at all, but my electronics knowledge is too inferior to really interpret what would cause this. My gut tells me some kind of short is to blame, but I have triple checked all the wires and solders and can't find anything. If I blew a 555 or transistor, would this cause a short internally, or would the component just not work?


Conclusion:
----------------------
I am okay with replacing components but would prefer not to replace everything if possible, and would like to know if the schematic is correct first before I risk blowing anything else. Sorry for the length of the post, but I wanted to make sure I provided as much information as possible about the situation so that anyone wishing to lend me a hand would be well informed. I hope I at least organized it somewhat coherently. Below this you will find links to my main components.

Thank you for any help that can be provided as I have spent way more time on this than I should have already! Also, thank you for your patience in looking at my diagram as I did not use standard symbols for my capacitors and potentiometers but I labeled them.


Components:
-----------------------------
LM555 Timers:
http://www.radioshack.com/product/index.jsp?productId=2062596

NPN Transistors:
http://www.radioshack.com/product/index.jsp?productId=2062586

Piezo Siren with built in driver circuit:
http://www.radioshack.com/product/index.jsp?productId=2062405

CR2032 3V/225mAh Lithium Coin Cells (I use 2 for a total of 6V or so):
http://www.radioshack.com/product/index.jsp?productId=3802113

Resources I used:
------------------------------
This prevents the first 555 from starting when power is turned on:
http://home.cogeco.ca/~rpaisley4/LM555.html#10
(LM555 Power-Up Reset Method 2)

Here's where I got information on how to use NPN transistors as NOT gates, as AND gates, and as a switch:
http://www.kpsec.freeuk.com/trancirc.htm

.

 

Until some one else who knows more comes along look at these items.

Schematic shows Pin 4 and 5 "floating" (not connected).

Pin 4 (reset) should be connected to +Vcc (6V).

Pin 5 (control voltage) should be connected to ground through
a .01uF cap.

Add .1 uF cap as close to Pin 8 as possible from pin 8 to ground as a
"decoupling" or "bypass" capacitor.

See datasheet for 555 for details: www.national.com/ds/LM/LM555.pdf

You may want to put them chips in an IC socket so you can solder the
socket to board before installing ("plugging in") chip to avoid the possibility
of damaging the chip when soldering.

My .02 Hope this helps.

 

What is this circuit trying to do?

Your schematic is pretty good, but there is a knack to making it easy to read. I think I see a monostable early on, but then I gave up for now.

 

Sorry for the confusion, the transistors make things kind of confusing.

The first 555 (reading left to right) is a monostable oscillator which counts from 30 to 60 seconds or so based on the pot's position whenever the button is pressed. There is a transistor NOT gate receiving the signal from this, so it outputs a high signal any time the first 555 has not yet been triggered, or has already finished its sequence.

After the transistor NOT gate following the first 555, the signal is passed to power pin of the second 555, which is acting as an astable oscillator. This one stays high for 2.5 seconds or so, then goes low for .5 seconds or so. I want the siren to be activated only for short bursts, so I use another transistor NOT gate to get the opposite signal from the output pin.

From here, I use a transistor AND gate to compare the output from the NOT gate following each 555. If the output of both NOT gates is high, then the user has either just turned on the circuit, or the first 555 is done with its counting sequence. Either way, I want the siren to turn on. The siren is basically always running off the second 555 astable oscillator unless the first 555 monostable oscillator is running its sequence.

Thanks for both of your help so far. I will look more into the datasheet that you have posted Pencil. The thing that confuses me most is that I had this working on a breadboard even with pins 4 and 5 floating, so that leads me to believe something may be fried and causing a short if that is possible.

 

Do you have access to a lab power supply? Powering a new circuit from batteries straight away is not a good idea, since there is no visual feedback of any problems like shorts etc. If you don't have acces to a psu, then I suggest putting a multimeter in line to measure the current. This is just to make sure there are no short circuits.

Next, measure the voltages on the IC's as well as the transistors. This will normally allow you to spot the culprit straight away.

 

Is there a requirement for the transistor inverters and the transistor and gates?

Attached is the application note and a datasheet for the 555

Your monostable (first 555) and the astable (second 555) are not typical.

You can use the reset pin on the astable to allowing it to drive the transistor for the piezo.

 

Do you have access to a lab power supply? Powering a new circuit from batteries straight away is not a good idea, since there is no visual feedback of any problems like shorts etc. If you don't have acces to a psu, then I suggest putting a multimeter in line to measure the current. This is just to make sure there are no short circuits.

Next, measure the voltages on the IC's as well as the transistors. This will normally allow you to spot the culprit straight away.

Unfortunately I don't have access to a lab power supply. I will try using the multimeter in line and see what I can figure out, thanks!

Is there a requirement for the transistor inverters and the transistor and gates?

Attached is the application note and a datasheet for the 555

Your monostable (first 555) and the astable (second 555) are not typical.

You can use the reset pin on the astable to allowing it to drive the transistor for the piezo.

Actually, I would prefer to not use the transistor inverters and AND gates so the circuit would be more simple and take up less space but I didn't know of any way to do what I wanted without them. The AND gate is there to make sure that the piezo only receives power when the monostable timer's output is low and when the astable timer is low. The reason I want them both to be low is because I don't want the piezo to be able to be heard when the monostable timer is running. The reason I use a not gate after the astable oscillator is because I couldn't come up with a set of resistors/capacitors using an online astable oscillator calculator to get a low period that was longer than a high period. I was able to get a 2.5 seconds high to a .5 seconds low, but couldn't find a way to output 2.5 seconds low and .5 seconds high.

The schematics I based my monostable oscillator off of is this:
http://home.cogeco.ca/~rpaisley4/LM555.html#2
http://home.cogeco.ca/~rpaisley4/LM555.html#10 (I used the first link, then modified the schematic accordingly using the second link to prevent the monostable oscillator from starting its sequence on power up)

Then I based the astable oscillator off of this:
http://home.cogeco.ca/~rpaisley4/LM555.html#3

When you say they are not typical, are you saying that the site I received the information from is using a non-standard method? I will look into these datasheets and hopefully learn something from them.

Also, if I use the reset pin to send a signal to the transistor switch base to power my piezo, when does the reset pin go high in an astable oscillator? At the end of each high low cycle? Any idea how long it stays high for? Basically, I want the piezo to trigger for half a second or so, every few seconds (think of a tracking beacon).

The schematic I have posted was working perfectly on breadboard so I'm thinking I may have fried some component after soldering and testing with a battery, but I'm not sure how to test each component without de-soldering the whole board and starting from scratch on breadboard. If in the end the circuit is smaller/more efficient than it is now, that is fine with me as long as I can get it to work again eventually, haha. This device will be attached to a flying device, so the smaller weight/size the better. Thanks again for all of the help so far, I will start reading some more into these datasheets.

 

Your design, as illustrated in the original post schematic, is consuming alot of current. Your coin batteries were rated at 225 mAH and your circuit consumed over 200 mA. You wouldn't have much time with to check out how well the circuit worked. Your buzzer consumes approx 150 mA and your circuit consumes 120 mA ... totally 270 mA and greatly reducing your time on batteries. You can get the circuit down to less than 30 mA and that would make your total consumption about 180 mA, still slightly over an hour with those two batteries.

There are errors in the schematic you provided. I don't want to point each error out, but some were already mentioned.

I'll give you some time to read the datasheet and the application note before continuing with a simplier design ... two 555 times and one transistor as the active devices.

Your coin batteries might be too far gone so you might want to use the breadboard's power supply for testing before putting in two new coin batteries.

Do you have access to an oscilloscope and multimeters?

 

Personally I have no problem with batteries, but I prefer "AAA" or "AA" for prototypes. I still haven't had a chance to look at it (I will try). I've had one hour of sleep with the promise of maybe 4 more before I go to work.

Have you seen my experiments?

Bill's Index

The 555 Projects

 

I want to once again thank everyone for all of the help and support that has been provided so far. I have been going over all of the documents posted and doing some more research of my own in an attempt to simplify my circuit somewhat.

I have changed the circuit up quite a bit from the previous version:

- I am now using a monostable "delay on" as referenced here: http://clarkson-uk.com/555-timer/operation/frames3.html
This provides me with the ability to have the output remain low until the timer sequence is complete, and then the output remains high indefinitely. This removes the need for the first transistor not gate I was using. Since this circuit is activated immediately on power up and I was having issues trying to adapt the examples on how to prevent power up monostable timers from starting, I just decided to scrap the whole push button idea and have the monostable time delay begin as soon as the switch is flipped to power up everything (except the LED which I have made parallel in order to allow it to be used without the siren).

- I have added the decoupling 1uf capacitor as suggested, along with the .01uf capacitor from control voltage to ground. I was only able to add these to the monostable oscillator because the astable oscillator receives its power from the output pin of the monostable oscillator, and I wasn't sure if I should decouple this or not. I also left out the .01uf capacitor from control voltage to ground on the astable oscillator because there is already a 33uf capacitor used in the timing sequence, so I thought it was kind of extraneous to add the .01uf capacitor as well.

In trying to only use 1 transistor, I have been pulling my hair out trying to figure out how to pull this off. I tried to figure out how I would go about wiring the piezo transistor to the reset pin on the astable oscillator like Joe suggested, but after reading through all of the documents and doing some searching I still haven't been able to figure this out.

I eventually figured out a PNP transistor instead of a NPN would provide me with the ability to power the piezo siren circuit when the astable output is low, removing the need for the second transistor not gate I previously had. Does it look like I set this up correctly?

The one main thing I'm not sure of, is whether the siren will be heard when the output from the time delay monostable oscillator is low.
I want the siren to always be silent while the monostable is low, but can't think of a way to do this other than an AND gate.

Thanks again for all of the help, I have attached my latest circuit diagram. I hope this one is a little easier to read/understand and has less errors than the previous one.

.

 

I hate to say this, but I see a problem. A standard 555 can only get within 1.2VDC of the Vcc power supply, it has to do with how it is build. A CMOS 555 doesn't have this problem. Note the internal diagram of a 555...

It looks a lot like this working with it...

It means the PNP will never completely turn off. You can add a couple of diodes to reduce this, redesign the driver, or use a CMOS 555, which doesn't have this problem. It doesn't have much drive either, but the transistor should take up the slack.

BTW, using the img and /img commands between brackets you can do this...

Just put the web address between the commands. You click on the thumbnail and the address comes up.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=20739&d=1277883503

 

In trying to only use 1 transistor, I have been pulling my hair out trying to figure out how to pull this off. I tried to figure out how I would go about wiring the piezo transistor to the reset pin on the astable oscillator like Joe suggested, but after reading through all of the documents and doing some searching I still haven't been able to figure this out.

It was never suggested to wire the piezo to the reset pin. What was suggested was to use the output of timer 1 to the "reset" pin of timer 2.

Have you design specifications changed?

Your astable in this new diagram doesn't seem to work.

Why do you have SW2? If you move the connection of the Power On LED to after SW1, switch 2 is unnecessary.

I want the siren to always be silent while the monostable is low, but can't think of a way to do this other than an AND gate.

Yes it can.

Main Function of Circuit:
----------------------------
1) User switches power on to circuit.
2) Piezo siren triggers every few seconds for .5 seconds or so
3) User adjusts potentiometer to set a time limit from 30 to 60 seconds.
4) User presses a button which starts the first 555 timer as a monostable oscillator and stops the piezo siren from going off.
5) After the first 555 timer sequence is complete, the second 555 timer is triggered as an astable oscillator to start, this powers a piezo siren every couple of seconds for a .5 second interval or so.
6) User turns off power to circuit and siren doesn't play anymore.

Your circuit continuously has the piezo energized until you press the button to trigger the monostable and then it's silenced for the period of the monostable.

You can not trigger a piezo siren every few seconds for a half second. Either the half-second is incorrect or the timing of the astable is off. Right now, your piezo triggers approximately every 2.5 seconds with a 91% duty cycle signal.

Your original circuit does not stop except for the period of the monostable (30 - 60 seconds). It does not stop after a half-second as you desired.

If the siren is stopping, something else is causing it to stop.

Now if you want it to work per your specifications ... you'll have to firm up what you want. Specifically, the timings.

With three timers, which includes two monostables and one astable, you can:
1) switch the power on and no piezo siren.
2) Trigger the first monostable to start the sequence (silent for 30 - 60 seconds)
3) First Monostable triggers second monostable that sets the time the piezo siren is energized
4) Second Monostable triggers the astable which drives the piezo siren at the desired rate.
5) Piezo Siren goes silent awaiting the next pressing of the trigger switch.

Break this down to the four (five if you include the power on LED) circuits and work on each one individually till you get what you want.

On Edit ...

Your questions on the diagram:

When pin 3 is low, current flows through the piezo siren circuit? Yes.

Would pin 3 be low while the monostable oscillator is low? Yes

 

Bill, in the first schematic I posted I was having a problem with the switch transistor never fully turning off while the circuit was breadboarded as well but didn't know the cause, thanks to you now I do! This actually caused the siren to emit a quiet buzz instead of the very loud wailing that it normally does. It sounded very similar to an old fashioned wind up kitchen timer counting down, so that was actually a beneficial side effect to have while the first monostable was counting to let the user know that a countdown was in progress. Also, thanks for the tip about the img tags!


Joe, sorry about the confusion with the reset pin. I must have misread your post on that matter. My design specifications are not exact, as long as the basic function is performed. In my first circuit if I had run my monostable output to my astable reset, wouldn't this send the reset pin high while the monostable was counting, and then low when the sequence is complete- turning off the astable; however, this is the opposite of what I am looking for. When the output of the monostable is high, I need a low signal running to the reset on the astable to keep it disabled. I could be reading the 555 documents wrong, but this is how I interpreted how the reset input and what you are suggesting would work.

It might help if I go into a little more detail as to what this device will be used for:

In my first post, you can see a green disc below the circuit. I am trying to create a small circuit that can be attached to a frisbee golf disc. This will be turned on, either triggering a countdown by just being turned on or by a push button switch grounding the trigger (whichever is easiest). The piezo astable can be on or off before the first monostable begins, I am impartial to this as well. The main thing is that when the monostable starts, I want the piezo siren to be quiet, or at least to have a small current flowing into the base of its switch which caused "kitchen timer buzz" that I experienced in my first circuit breadboard. Actually, I would prefer to have this buzz during the monostable countdown if possible so the user knows the circuit is actively counting if possible. Other players will be throwing their discs as well, so I don't want the siren annoying them until everyone has had a chance to throw.

To start, the user will turn on the circuit, start the monostable countdown, throw their frisbee golf disc, and then after the time period of 30-60 seconds, the siren will go off every 2.5 seconds for .2 seconds like a tracking beacon so the user can find their disc if it ended up somewhere in the woods. After the monostable timer completes its sequence, the astable needs to remain running until power is turned off to the circuit. I also sometimes play at night (but not always), which is why I have the LED parallel with its own switch as opposed to it being behind S1. The purpose of this LED is not to show that power is on, but to light the disc in flight to aid in tracking it during night play.

Now that you have mentioned it though, I really should have some method of alerting the user that the batteries are not dead before they throw their disc, so I would either need the siren buzz resulting from some current reaching the transistor switch during monostable timing sequence, or I'll just add one of those really tiny red led's to light up during the monostable timing sequence.]

As far as the timing goes with the astable circuit, I was just estimating the time in my first post. I have since calculated the exact timing I used in my first schematic to high 2.5 seconds, low .2 seconds. The astable circuit in my second diagram is exactly the same as in the first diagram unless I redrew it incorrectly.

Since I want the astable oscillator to continue running its sequence until the user finds their disc, I could probably get by with only 2 555s right?

The main thing here is minimizing size and weight so as to minimize the effects of the circuit on the performance of the disc. My timings and specifications aren't exact because I don't really know what I'm doing here, so if I'm making it overly complex for no reason and there is an easier way I am open to ideas. I just want a 30 to 60 second monostable count down, which starts an astable oscillator which continues indefinitely until power is turned off. If I could have the transistor switch cause the siren to buzz like I mentioned during countdown, that would be ideal unless you think that isn't a good idea and I should just use an indicator LED so the user knows their countdown is going.

I just picked up some new components because I'm assuming I must have fried some of my originals in my soldering fiasco. I guess I'll try breadboarding my new design out section by section and see what happens.

Thank you both for all of your detailed help thus far. I hope I am not trying your patience!

 

Ok ... using your stated specifications,

To start, the user will turn on the circuit, start the monostable countdown, throw their frisbee golf disc, and then after the time period of 30-60 seconds, the siren will go off every 2.5 seconds for .2 seconds like a tracking beacon so the user can find their disc if it ended up somewhere in the woods. After the monostable timer completes its sequence, the astable needs to remain running until power is turned off to the circuit. I also sometimes play at night (but not always), which is why I have the LED parallel with its own switch as opposed to it being behind S1.

You have two timers, one monostable and one astable. You have one buzzer driver, and one light for nighttime playing. Four circuits in all.

The buzzer driver should go back to the NPN (2N4401), but the base resistor is too high, not allowing the transistor to saturate completely.

The white light ... how did you choose the 150 ohm resistor as the series resistor?

The astable oscillator needs work. It won't oscillate as drawn. You want the output to be positive for 0.2 seconds and off for approximately 2 seconds.

 

The white light ... how did you choose the 150 ohm resistor as the series resistor?

I used this LED calculator: http://led.linear1.org/1led.wiz

Is 150 omhs not correct? The specs on the LED are as follows:
5mm White LED - 3.3Vf @ 25mA


I ended up recreating each section on my breadboard and managed to get each individual section working. When trying to combine the two timers, I ran into some problems but eventually managed to get everything working exactly the way I want it to. Whether or not it is the most efficient way, I'm still not sure, but it is working better than my original breadboard circuit and is using 3 less transistors, so that is good.

Here is my latest schematic:

The reason the 200K Ω Resistor before the pot says optional is because this number is something I want to play with out in the field before I make a final decision on whether or not I want to have a base time limit (say 5 seconds) plus the 0-40 provided by the potentiometer, or if I want the option to be able to set the timer countdown to 0 so the astable is immediately oscillating when the circuit turns on until it is turned off. Having an option to set it to 0 might be nice for night play so I can hear where it is flying towards if I lose sight of it.

In order to hold the astable oscillator high, I ended up coming up with something on my own that I'm not sure is the best method. I used a 100k resistor between the output of the monostable and the trigger of the astable. When the output from the monostable is low, this means the timer is counting down.

This is holding the trigger low on the astable as well. While the trigger is held low, the astable's output remains high and doesn't go low until the output from the monostable goes high. It works, but also seems to effect the timing of the astable as a side effect. The high time of the astable seemed to be shorter than before, so I increased the resistor from pin 8 to pin 7 to 270k from 100k and now it sounds perfect.

I also added a new "Delay Indicator LED" so that the user knows when the circuit is counting down.

Everything seems to be working perfectly. I adjust the pot which gives me a range from 0 to 40 seconds. I turn on the circuit, and the delay indicator LED turns on and no siren can be heard. Next, after the time runs out, the astable begins its sequence and the siren is triggered every couple seconds until I turn it off. I can also turn on the Bright White LED to light the frisbee as desired.

If there aren't any major flaws that anyone can see, I'll probably stick with this design because I'm really itching to get out and give it a test run in the field. Once again, in function- this is working exactly as I want it to. I don't want to make the same mistake and solder this all down before a pro can take a look at it though in case I have made some horrible mistake that will cause something to burn out after extended use. I have only powered the circuit on for a few minutes at a time so far.

I can't express my gratitude enough to everyone for all of the help that has been provided, and a special thanks to JoeJester and Bill_Marsden for all of the detailed help and having the patience to deal with my incompetence . I'm actually down in Houston, so if either of you two ever make it down this way, look me up and I'll treat ya to a steak dinner for the help.

Also, I'll probably use a 556 to save space/money when I actually get down to soldering everything on to my board. There shouldn't really be any schematic changes necessary though other than the pin numbers being different, correct? (other than the obvious that on the 556 there is only 1 Ground pin and 1 Vcc pin as opposed to 2 of each using 2 555s)

.

 

So you changed your specs to zero to whatever, vice 30 to 60.

Your astable oscillator is very unorthadox. It has not worked from a simulation point of view (can not find operating point) because of the way you've worked the Vcc pins. It may have worked by the breadboard, but without an inspection of that, the reason it's working is unexplainable by me. So that circuit is untenable in my point of view.

You could have stuck with positive logic and reduced your parts by the two "inverters". You jumped back into the inverters because you know them and it satisfies your immediate need of fast production.

I would move your "indicator" LED to the astable for two reasons, you'll see the pulsing and you can reduce the LED current to 15 mA or 10 mA which will still make it bright at night -- and you'd save some energy on your coin cells.

Anyway, attached is what I did from your original specifications then I removed the optional resistor prior to this posting.

 

Whoops! I apologize. I used all of my small jumpers on my first soldered board so I am left with only longer ones and it makes it hard to draw the schematic from the breadboard. I accidentally left off the Vcc lead to +6v on this latest schematic. I have added it and here is the fixed version. I am pretty sure this is how it is on the breadboard now, but I'll have to go get another pack of jumpers later to make reading my own breadboard a little easier.

(This is just the previously uploaded schematic with the Vcc fixed)

Also, in my latest version I removed the diode from trigger to ground on the monostable because I read that only really helps to discharge the capacitor to allow quick re-triggering which I won't need. Does this serve any purpose other than that, or would I be safe removing it?

Thank you very much for your diagram! One thing I am unclear about is the TMR1 and TMR2 off of each output pin. Additionally, on your schematic would the indicator LED only blink after the timer runs out? I would like the indicator to be on while the monostable is counting down and then after that it turns off. This is just so the user knows the timer is actively counting down and the circuit is powered. And finally, the only reason I'm using the inverter for the astable is because I haven't found any other way to obtain a short burst from a 555. Everywhere I've looked has said it is impossible to get a longer low output than high output. The main reason I only want to turn the siren on for .2 seconds or so is because at this amount of time, it produces a "PEEEE EWWW WHOOP" sound and then stops. It sounds very similar to a person whistling to get your attention and less like a smoke detector going off. I don't want to scare people with my siren and have them think someone's car alarm is going off or similar, but a short "whistle" would be nice.

I'll try assembling your circuit on my breadboard and see how it functions differently. Before this, I'll take a current reading with my multimeter so I can compare the savings. Thanks again!

 

The tmr1, tmr2, as well as the AM1 through AMx are just test points for me to see the expected signals in the simulation program.

You know, the LED change was a suggestion, there is nothing hard and firm about anything in the project section. I only made the suggestion from the energy conservation point of view. You know the astable can not work without the monostable being high.

This is just so the user knows the timer is actively counting down and the circuit is powered.

Your monostable doesn't count down, it stays high. Nothing is counting down. If you needed a count down timer, that's another circuit ... or more.

As far as current readings go ... if your using a digital, you might not see the peak current from the 0.2 second pulses. If you have a peak hold function on the meter, you'll be in good shape. If you have an analog meter, you might see a flicker when the 0.2 sec pulse appears. Using the duty cycle figure you can estimate the current being drawn.

Have fun.

 

Ah I see. As far as calling it a countdown, I know it's not actually a countdown timer, but that's just the way I think of it since after it counts to a set time, it activates the second circuit. Thanks again for all the help!