PedalSHIELD UNO Please Help with reading a schematic arduino UNO

[jimitrader]

Quote from: jimitrader on February 02, 2018, 12:38:27 PM<blockquote>

[jimitrader]

 





I put c11 to ground
Pin 4 to ground
5v to pin 8


for the Arduino connectors I put digital ground -jumper-ed over to analog ground... then analog ground #2 to the breadboard ground.
all other ground symbols to ground

[potul]

All what you describe looks ok to me. What is the problem you are having?

[jimitrader]

jacks are mono...I talked with company yesterday

[jimitrader]

does anyone know what the readings on the op-amp pins should be?

[ElectricDruid]

With no input, the input stage is biased to that 2.5V virtual ground, so it should be at 2.5V. With no input, the output of that op-amp should be the same as the input, so that pin and the -ve input should both be 2.5V too.

Same logic applies for the output stage - with no input signal, you should get a midpoint voltage from the PWM, so 2.5V. That stage is set up as a voltage follower, so the output and the -ve input are both 2.5V too.

Please someone step in and correct me if you spot something wrong in this line of reasoning, but it looks to me like you should have 0V and 5V on the power pins and 2.5V everywhere else.

Which op-amp are you using? Not everything will cope with a 5V supply.

Tom

[jimitrader]

Pin readouts:
1  1.08
2. 1.10
3. 1.00
4. 0.00
5. 2.57
6. 2.80
7. 2.77
8. 5.54

I am using the TL972 op-am ic

any thoughts? thanks JL

[ElectricDruid]

The output op-amp is about right, but the input op-amp is terrible. The input is way low. That's where you need to look.

T.

[potul]

The output op-amp is about right, but the input op-amp is terrible. The input is way low. That's where you need to look.

Isn't it the other way around? According to the schematic posted pins 1,2,3 are the output opamp and pins 5,6,7 the input one.

Pins 1,2,3 are way too low. On the other hand... how is the output opamp biased?

[ElectricDruid]

The output op-amp is about right, but the input op-amp is terrible. The input is way low. That's where you need to look.

Isn't it the other way around? According to the schematic posted pins 1,2,3 are the output opamp and pins 5,6,7 the input one.

Yes, it is. Sorry, my mistake. It's the output one which is wrong. I replied quickly and didn't check the schematic again.

Pins 1,2,3 are way too low. On the other hand... how is the output opamp biased?

It's fed a 0-5V signal from the PWM output - that's directly DC coupled, so the bias is included on the PWM output.

That suggests that perhaps the Arduino is not outputting the PWM that it should. Perhaps the circuit is ok and this is a firmware issue?

Tom

[jimitrader]

what could cause the pins 1,2,3 to be so low? i re made it 3 times and am really sure i have it all connected right...double checked the code and tried with different uno...still nothing..hmmm

[potul]

I would check the software to verify that the PWM output is working as expected.
Try to modify the code to send a fixed value through the PWM and verify what you get out of the Arduino

Do you have a scope?

[jimitrader]

I would check the software to verify that the PWM output is working as expected.
Try to modify the code to send a fixed value through the PWM and verify what you get out of the Arduino

Do you have a scope?

No I don't have one(scope)...I have used the board for other testing and i know that it is ok...when you say software are you talking about the code? thanks JL

[potul]

yes, I mean the code

[ElectricDruid]

what could cause the pins 1,2,3 to be so low? i re made it 3 times and am really sure i have it all connected right...double checked the code and tried with different uno...still nothing..hmmm

Aside from the code, the only thing I can see is that one of those two capacitors to ground could be faulty. It's pretty easy to "overcook" them when soldering, especially if they are film caps. I've frazzled a few like that, and then you can get shorts inside the cap itself.

HTH,
Tom

[jimitrader]

I am trying to build on breadboard...no soldering yet...I will double check the caps...and the code...thanks JL

[potul]

I would definitively do some code debugging. If the PWM is not working, you will probably get low voltages there.

Try to code a tone generator that simply outputs a sine wave or similar.

[jimitrader]

I would definitively do some code debugging. If the PWM is not working, you will probably get low voltages there.

Try to code a tone generator that simply outputs a sine wave or similar.

the volts from my usb ports are 6.8v and out of the Arduino about  6.12? seems kinda high shouldn't it be 5 on both?

what would cause that?

maybe that is part of the problem?

[jimitrader]

Solved!!
I was using the wrong code!! Thanks potul!!after reviewing the site again I noticed the code i was using was the sample code..after finding the real codes everything is sounding good now...Thanks for all the tips...JL

[potul]

Good to know you could solve it. Once you have something interesting coded, show us the result!