Yes, connect them like this:

I looked over the datasheet for the chips and couldn't find any mentioned of resistors coming out of the chips, but it looks like standard resistor symbols. Any input/clarification on if those are restistors called out? If so, would the size/specs of 7-seg displays selected be the deciding factor for reistance size?

Thanks,
Steve

 

The resistors are required to limit the current flow through the LED displays, and thus the 4543 IC.

The 7-segment displays shown are common anode. Each cathode must have a resistor to limit the current in each segment. You'd usually want something like 10mA-12mA per LED segment. The exact value of the resistor will depend upon the supply voltage you will be using, and the 7-segment display forward voltage at that current.

 

The resistors are required to limit the current flow through the LED displays, and thus the 4543 IC.

The 7-segment displays shown are common anode. Each cathode must have a resistor to limit the current in each segment. You'd usually want something like 10mA-12mA per LED segment. The exact value of the resistor will depend upon the supply voltage you will be using, and the 7-segment display forward voltage at that current.

UGHH!!! Thanks for being patient with me. By my own admission I am very raw, but I should have known that from the many "trial" run with a simple LED. D'oh.

I am slowly sinking in this project of mine. I have been trying to keep moving on and I have a new circuit for you to hammer on.

I have many questions so I figure I will just get most of them out and take the feedback, regardless of how embarrassing my lack of knowledge/understanding is on most of this stuff is.

You will notice I did redraw the circuit with the 741. I think the 555 cushion(1/3 - 2/3) was causing me some sensitivity issues. I setup the circuit as shown (except only 1 741 and NO 4553) for the kids tonight and the buzzer responded very well every time the kids broke the laser. I hope I can dial in the sensitivity more with the pot. (a few times my daughter did break the laser very, very quickly and the buzzer did not sound.

I have tried to read up on the use of SCR's. I was planning to just use latching push-on/push-off switches, but the sizes of those types I have been able to find are quite small. I have found some extra large, illuminated "game" buttons that are Mom. Close, NO. I would use that style to trigger the gate. I am less concerned about the reset button "look". I plan to use a Mom. Open, NC.

SCR Questions: I have scanned the forums for help so I do not look completely ignorant. I have seen mention/suggestion of using a diode between the gate and switch. I do not understand why that is necessary? Doesn't the SCR already have a "one-way" system built in?

741 Output Voltage Question: I was just getting familiar with the 555 and the -1.7V at the output. I made a single 741 circuit as shown with a 9V supply voltage and measured the output voltage at 6.8V with my meter. I then turned the light on (buzzer off), but still measured 1.28V at output. I really did try to check the datasheet to understand what was happening, but I was treading water. Is there a similar "standard" drop like the 555's -1.7V or is there something else to be considered? Was the 1.28V measured operator error? I know I will need to have a clear understanding what my output voltage will be for the Clock Input and Alarm circuits.

General Question 1: As I have mentioned, I have only prototyped 1 741 circuit. I have drawn a second 741 mostly to ask if that type of setup would be doable? Could I use a 339? Quad and have 4 separate sensing circuits? Could/would I just add diodes coming out (once I get a better understanding of the output voltage, I expect some sort of resistors as well?) before coming together into the clock/alarm stage?

I have looked over many circuits and I see many people suggesting caps, but I will admit I am very unsure when/why to use them in some of the places mentioned.

General Question 2: I have used a standard 741 circuit I found as the starting point for this. I have found some circuits that add a 3rd resistor after the pot. What would be the purpose of the 3rd resistor? The combination of 2 resistors into each pin (2 and 3) are meant to provide a voltage divider correct? Stupid question time - what would be the effect of just using a pot. vs. LDR? Would the 741 not be able to use the single pot. as the ref and then the change in resistance of the LDR would drop/rise above the ref?

I am off to bed. I will look forward to any help any of you can offer.

 

UGHH!!! Thanks for being patient with me. By my own admission I am very raw, but I should have known that from the many "trial" run with a simple LED. D'oh.

That's perfectly OK. Better that you asked up front than burned something up! No harm, no foul.

I am slowly sinking in this project of mine. I have been trying to keep moving on and I have a new circuit for you to hammer on.

Slow and steady wins the race.

I have many questions so I figure I will just get most of them out and take the feedback, regardless of how embarrassing my lack of knowledge/understanding is on most of this stuff is.

No reason to be embarrassed; you're new at this. What's embarrassing is when I make a mistake on a simple circuit - I've been doing this too long for stuff like that.

You will notice I did redraw the circuit with the 741. I think the 555 cushion(1/3 - 2/3) was causing me some sensitivity issues. I setup the circuit as shown (except only 1 741 and NO 4553) for the kids tonight and the buzzer responded very well every time the kids broke the laser. I hope I can dial in the sensitivity more with the pot. (a few times my daughter did break the laser very, very quickly and the buzzer did not sound.

Well, the 741 was the greatest thing since sliced bread when it was introduced - over 40 years ago. Nowadays it's sort of like a Chevrolet Corvair. It might get you there, but you'd rather be driving just about anything else.

You should consider using comparators instead, like the LM339 quad comparator. Opamps are used when you want an analog response to an analog input. Comparators are when you want a yes/no type output.

On adding more channels ... you should be able to use just one threshold divider to set the trip level for all of the LDRs, rather than one per channel. You could just use a 10k pot, wire one end to ground, the other end to +V, and take the inverting input (-) from the wiper.

One important difference to keep in mind is that the LM339 can only sink current from its' output - it cannot source current. So, it requires that you use a pull-up resistor on the output in order to produce a voltage.

I have tried to read up on the use of SCR's. I was planning to just use latching push-on/push-off switches, but the sizes of those types I have been able to find are quite small. I have found some extra large, illuminated "game" buttons that are Mom. Close, NO. I would use that style to trigger the gate. I am less concerned about the reset button "look". I plan to use a Mom. Open, NC.

OK, that's fine.

SCR Questions: I have scanned the forums for help so I do not look completely ignorant. I have seen mention/suggestion of using a diode between the gate and switch. I do not understand why that is necessary? Doesn't the SCR already have a "one-way" system built in?

SCR's are covered in our E-book: http://www.allaboutcircuits.com/vol_3/chpt_7/5.html
You should have a look there if you haven't already.

Diodes are used when AC is the input. If the supply is DC, you won't need it.

741 Output Voltage Question: I was just getting familiar with the 555 and the -1.7V at the output. I made a single 741 circuit as shown with a 9V supply voltage and measured the output voltage at 6.8V with my meter. I then turned the light on (buzzer off), but still measured 1.28V at output. I really did try to check the datasheet to understand what was happening, but I was treading water. Is there a similar "standard" drop like the 555's -1.7V or is there something else to be considered? Was the 1.28V measured operator error? I know I will need to have a clear understanding what my output voltage will be for the Clock Input and Alarm circuits.

The 741 is really old, and you shouldn't plan on it being able to get within a few volts of either supply voltage for the inputs, or within about 1.5v of the output.

Comparators will sink current down to within ~0.3v of the rail, depending on the sink current. Note that the LM339 should be limited to ~6mA sink current maximum, as 6mA is the minimum guaranteed sink current; if you want to be certain that your circuit will work, you need to stay at/below that.

General Question 1: As I have mentioned, I have only prototyped 1 741 circuit. I have drawn a second 741 mostly to ask if that type of setup would be doable? Could I use a 339? Quad and have 4 separate sensing circuits? Could/would I just add diodes coming out (once I get a better understanding of the output voltage, I expect some sort of resistors as well?) before coming together into the clock/alarm stage?

The 339 would be better. The 339 output can be used to sink current from a PNP transistors' base via a resistor, and the PNP transistor can source the current to your buzzer.

I have looked over many circuits and I see many people suggesting caps, but I will admit I am very unsure when/why to use them in some of the places mentioned.

Have a read through this "sticky" thread:
http://forum.allaboutcircuits.com/showthread.php?t=45583
If you don't use bypass caps, you will likely wind up having strange problems.

General Question 2: I have used a standard 741 circuit I found as the starting point for this. I have found some circuits that add a 3rd resistor after the pot. What would be the purpose of the 3rd resistor? The combination of 2 resistors into each pin (2 and 3) are meant to provide a voltage divider correct? Stupid question time - what would be the effect of just using a pot. vs. LDR? Would the 741 not be able to use the single pot. as the ref and then the change in resistance of the LDR would drop/rise above the ref?

THe 3rd resistor is a safety to ensure that there is always some minimum resistance in the series string.

For example, without that 3rd resistor, if you had the pot turned as low as it could go (~0 Ohms), and then the LDR was exposed to bright light, it would also go to a very low resistance - so you would basically have a short circuit across the supply, and the LDR would get fried to a crisp. The 3rd fixed resistor prevents such a mistake from creating smoke.

 

Yes, connect them like this:

I have ordered enough parts to be dangerous. I now will wait patiently for delivery and then proceed with the utmost caution.

I have several threads going about different aspects of the same project because I am trying to keep the topics relativley separate. Unfortunately, I have to mix them up with my next question.

I plan to use the above circuit as my "Strike Counter" - counting the number of times the kids break a laser. My sensor circuit will feed Pin12.

In a separate thread, I had asked for some guidance on a standard/regular seconds counter because the prices I found were crazy. Elec mech suggested Bill's 1-second clock circuit. I know this may be painfully obvious, but I would just make a second circuit like attached above and instead of feeding my "Sensor" into the clock input (pin 12), I would use Bill's circuit as the pin 12 feed? I plan to leave off the entire bottom section of Bill's circuit (minutes/hours not needed for my application). I would still be able to count up to 999 seconds?

Thanks

 

Sure, that will work.

Note that you will want to connect the STROBE/LE input to ground, and RESET should be kept low unless you wish to reset the count to zero.

 

Sure, that will work.

Note that you will want to connect the STROBE/LE input to the voltage supply (+V), were RESET should be kept low unless you wish to reset the count to zero.

SgtWookie - Based on the info from Zod (when discussing the sensor/strike counter), I thought the Strobe would be to ground? Then I could just use a reset button to the reset pin to reset the strike counter. I was thinking a similar setup for the time display as well.

Now, I am confused on how for sure to set the Strobe and Reset pins. In real life, I would want both the strike display and time display to keep the "strikes" and "time" until I reset them.

Help ....

 

Sorry, I have corrected my post. Zod told you correctly.

Use a 10k resistor from each RESET to GND to keep them from randomly resetting. Use a N.O. pushbutton connected from +V to each RESET to reset them.

 

Thank you!