I am filled with contrition. Please forgive my lapse.

hgmjr

Ha !
Wish I had half your knowledge.

OK, will be off-line for awhile doing the mechanics stuff, etc.............
Tx's everybody,
Oxbo

 

Ha !
Wish I had half your knowledge.

Your expertise and skill are elsewhere. I have never welded a thing. I would do myself a serious injury were I to attempt such a dangerous activity.

hgmjr

 

Hey Oxbo,
On this schematic:

You're showing 2.9v above R3. Does that mean you're measuring 2.9v across R3 to R9, or are you measuring 2.9v from the high side of R3 to ground?

If you are measuring 2.9v across R3 to R9, then since I=E/R, 2.9/120 = 24.16mA. This really isn't too bad because they are multiplexed.

If you are measuring 2.9v to ground, then you also need to subtract the Vce of the ULN2804, which should be around 0.65v, from the 2.9v - that leaves 2.25v, which means 18.75mA current through the LED segments - which is just fine.


The 360 Ohm resistor needs to be 1/4W.

 

You're showing 2.9v above R3. Does that mean you're measuring 2.9v across R3 to R9, or are you measuring 2.9v from the high side of R3 to ground?

If you are measuring 2.9v across R3 to R9, then since I=E/R, 2.9/120 = 24.16mA. This really isn't too bad because they are multiplexed.

If you are measuring 2.9v to ground, then you also need to subtract the Vce of the ULN2804, which should be around 0.65v, from the 2.9v - that leaves 2.25v, which means 18.75mA current through the LED segments - which is just fine.


The 360 Ohm resistor needs to be 1/4W.

That was "Across" R3 Sarge.
I saw that too, and also considered that it would probably be OK (promising myself to take a closer look at it come fabricating time).
Thing about it is, this Fluke 73 digital multimeter I have is always bouncing around at the tenth's scale, I can't recall exactly what it'd say, 2.8, 2.9, 2.7, 2.9, 2.8 etc, etc, etc.
It's aggravating to say the least. seem like I'm always having to round off/take my best guess.
And, measuring current, it would only show a 0.02, not a 0.0204 or something like that.
There was one where it'd show a 0.01 then blink to 0.02 then back to 0.01, etc, so I'd have to presume that it was right there on the high side of 0.01 and then round up to 0.02 as, that's what the math predicted, etc, etc..
And looking for ua's, forget it, got 0.0, even punching the little button to manually change ranges= no diff......
So am not comfortable with the meter at all, just too much fluctuating around.
I haven't gotten this Simpson yet, maybe Monday, but I sure hope it is in good shape, It'll (hopefully) give me better readings without all the jumping around nonsense.
That's why I went online and got it (Simpson analog), am tired of nervous digital meters !

EDIT : Just was reading the manual, says it only measures 32ma -to 320ma, plus up to 10A.
POS mo-yawn crap, gonna throw it in the river ! ! !

 

The Simpson 260 is a good piece of equipment, but you have to keep in mind the Ohms per volt. In the case of the Simpson 260, it's 10k Ohms per volt. If you're dealing with a low-impedance circuit, the impact will be insignificant - but if you're measuring across, say, a 50k resistor and reading 5v, you must keep in mind that the Simpson will have an impedances of 10k Ohms/volt, so in parallel with the 50k resistor, you'll have a total of 25k - which can upset the balance of the circuit.

Digital multimeters have an extremely high input impedance (tens of megohms) so they have a minimal loading effect when measuring voltages in a circuit.

 

The Simpson 260 is a good piece of equipment, but you have to keep in mind the Ohms per volt. In the case of the Simpson 260, it's 10k Ohms per volt. If you're dealing with a low-impedance circuit, the impact will be insignificant - but if you're measuring across, say, a 50k resistor and reading 5v, you must keep in mind that the Simpson will have an impedances of 10k Ohms/volt, so in parallel with the 50k resistor, you'll have a total of 25k - which can upset the balance of the circuit.

Digital multimeters have an extremely high input impedance (tens of megohms) so they have a minimal loading effect when measuring voltages in a circuit.

Cheeez;
Too deep for me !
It'll either work or not, not going to be doing any super sensitive projects, etc.
What would be an example of a low-impedance circuit and an example of a high impedance circuit ?
I see it somewhat in your example above.
Will probably only use it in instances where the Fluke is suspect, etc.....

 

OK, let's say you used the Simpson to measure the voltage across R3, a 120 Ohm resistor, and you measured 2.9v.

2.9v x 10k = 29k Ohms in parallel with 120 Ohms. The loading effect in this case is negligible; as 120 Ohms is about 0.4% of 29k Ohms.

120 Ohms is a pretty low impedance.

 

OK, let's say you used the Simpson to measure the voltage across R3, a 120 Ohm resistor, and you measured 2.9v.

2.9v x 10k = 29k Ohms in parallel with 120 Ohms. The loading effect in this case is negligible; as 120 Ohms is about 0.4% of 29k Ohms.

120 Ohms is a pretty low impedance.

And for the next example ??

 

Do you expect me to go through every possible combination of resistance and voltage?

I ain't gonna do dat for ya...

 

Do you expect me to go through every possible combination of resistance and voltage?

I ain't gonna do dat for ya...

Well,
Am trying to discern the difference between impedance and resistance.
I know impedance concerning a speaker, impedance is measured in ohms, but somehow I connect impedance with coils/chokes etc, but, we never say the impedance of a relay's coil is such and such, we just say resistance.
Now you give me an example to do with measuring a resistor and refer to impedance.
Perhaps impedance has to do with the combination of resistance and voltage ?
Perhaps I need to go read up on impedance.
OK, thanks Sarge........
Oxbo

 

Project update ;
OK, have finally gotten all the hardware installed.
Have all the primary power wiring installed (cut to fit, etc).
Now the fun part, take it all apart and paint it..........
After this will have to fabricate the circuit boards for the team scores, period count, MPSA64's & limit resistors, and the buzzer relay board,
then, do the 25 pin socket and data lines.
Still, a ways to go ..........
Have a nice day,
Oxbo

 

OK;
Ducks starting to line up.
Am going over tonight to retrieve the console from my son.
Am going to hook up console to big board and check the voltages and see if they concur with the breadboard voltages we went through the other day
(chip drop, cable length drop, etc).
Then, start fabricating the circuit boards......
Have a nice day.....
Oxbo

 

Good afternoon forum folks;
I would like to put up this circuit for your pursual.
This is the circuit to drive/sound the "buzzer" for approx one second whenever the countdown clock reaches zero (or whatever the preset number is set at).
Theory is, when the clock reaches zero, it puts out a 5V 50ma signal that I have built a relay circuit to achieve such results (needed because the clock otherwise wouldn't stop, etc.
So, I have the stop happen and when this happens, I also wanted a buzzer to sound for approx one second. I had to build a circuit to accomplish this.
Now, looking at the circuit, just take my word for it, the input signal will be "ground".
Each and every time that input is grounded, the buzzer will sound for approx one second (actually 746ms).
I tried to utilize the 555 timer by having it's grounds not connected, then the input signal grounds it, but I found that upon power up the 555's output is high even without any grounds applied to it/and/or caps.
So, I had to add K1 to power the 555.
Would like any input on this configuration before I comit it to PCB.
The Power-on PB switch is just a NO push button switch that has a light in it that lights up when power is applied to the system, it also doubles as a NO PB of which I decided to use as another way to sound the buzzer (manual)
Tx's
Oxbo

 

Hi Oxbo,

Have a look at the attached. This timer won't start out with the output high when you first power it up. That's because the timing cap, C1, is connected to Vcc rather than ground.

When triggered by 5v to 12v being placed on the left side of R5, a negative pulse is coupled through C3, which triggers the start of the timer. The output of the timer stays high for 1 second, and then returns low.

 

Hi Oxbo,

Have a look at the attached. This timer won't start out with the output high when you first power it up. That's because the timing cap, C1, is connected to Vcc rather than ground.

When triggered by 5v to 12v being placed on the left side of R5, a negative pulse is coupled through C3, which triggers the start of the timer. The output of the timer stays high for 1 second, and then returns low.

Hi Sarge;
Tx's for the comeback, however,

I need to "trigger" with a GND being applied....
What happens if I get rid of R4 and Q1 and apply GND to the left side of C3 ?
What I want is, every time GND is applied, I get a 1 sec pulse from the 555, and, GND will be removed but no action happen, action happens only when GND is applied/reapplied, etc......

 

OK then - remove R5 and Q1. Change R4 to 10k, since you're using CMOS.

Place a momentary short from the junction of R4/C3 to ground to trigger it.

 

Shouldn't there be a diode coming off of 555-pin#3, cathode on coil side?
If not, please explain why some do, some don't.
Tx Yu ......

 

You're already losing at least 1.3v from your 12v by sourcing current from the 555 output, as the output stage is a Darlington follower, so without the diode you're left with around 10.7v.

Adding another diode in there would drop the relay coil's voltage another 0.7v or so, depending on the diode used; so you might get down under 10v. You would be getting to the point where reliable pull-in might not occur.

The extra diode really isn't needed anyway. The reverse-EMF diode across the relay coil takes care of the spike. If THAT diode is not there (missing or open) then you would have a problem. Use a 1N400x type diode, not a 1N4148/1N914 - the latter are faster, but have a far lower current rating.

 

Sarge;
Just finished building/testing the circuit you offered.
It was intermittent at best.
Most of the time it would "beep" when I applied GND (which is good), then sometimes it wouldn't beep when I removed GND (which is what I wanted) but most of the time it "WOULD" beep when I removed GND (leaving GND on for several seconds).
So, like the period count circuit you, Bernard, and I worked on so long ago, I need to choose the most reliable circuit,and, I believe the circuit I came up with is the more reliable one (never failed yet, plus, is not using pwr until signal comes in).
I would like to move on from here and fab the PCB for it according to my specs, etc (last board to fab).
Tx's for your help.......
Oxbo

(Just read your reply on the diode.......Tx's)

 

It's supposed to be triggered by the negative-going edge of the input pulse; when GND is first applied.

Go ahead and use the one that works for you. Keep in mind though, the relay is going to use power as long as the coil is energized.