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Input stage problems
5 years 4 months ago #1576
by carminacore
Input stage problems was created by carminacore
Hello everyone,
I got a little problem with the development of my pedalSHIELD implementation. Thirst thing to mention should probably be that I am not using Electrosmash PCBs as I am intending to connect it to an STM32 dev board later on. Two things I changed are LMC7660 instead of TC1044 and 1N5818 diodes instead of 1N5817. Both 1044 and 5817 were impossible to get somewhere around.
The problem is that I can't get a clean boost example to work. There is always a bitcrusher like overdrive in the background of the buffered input signal.
I have loaded both ADC and DAC check software to my chinese clone. DAC seems good - I can hear sinewave loud and clear. On the other hand ADC analogRead return values around 200 instead of 500. I have measured each and every U1 pin and everything except for pin 3 works fine. This one little buddy stabilizes at sth like 0.16 V, BUT the problem is that this is the case even without any Arduino at all. I can just provide 3.3 and 5V directly to the circuit and it will still be 0.16V. When I am measuring 1.6V test point on the other side of R2 it is ok.
Without any load, LMC7660 provides clear -5V. With a load (U1 and U2) connected, voltage drops (rises) to -4.35V. With just the U1 connected it is something around -4.75V.
Additionally, when I hit strings any harder than just touching them the signal gets overdriven as heck, and ADCs readings drop to 0.
Totally stuck at this one. Every idea will be appreciated.
You can see my little monster here
I got a little problem with the development of my pedalSHIELD implementation. Thirst thing to mention should probably be that I am not using Electrosmash PCBs as I am intending to connect it to an STM32 dev board later on. Two things I changed are LMC7660 instead of TC1044 and 1N5818 diodes instead of 1N5817. Both 1044 and 5817 were impossible to get somewhere around.
The problem is that I can't get a clean boost example to work. There is always a bitcrusher like overdrive in the background of the buffered input signal.
I have loaded both ADC and DAC check software to my chinese clone. DAC seems good - I can hear sinewave loud and clear. On the other hand ADC analogRead return values around 200 instead of 500. I have measured each and every U1 pin and everything except for pin 3 works fine. This one little buddy stabilizes at sth like 0.16 V, BUT the problem is that this is the case even without any Arduino at all. I can just provide 3.3 and 5V directly to the circuit and it will still be 0.16V. When I am measuring 1.6V test point on the other side of R2 it is ok.
Without any load, LMC7660 provides clear -5V. With a load (U1 and U2) connected, voltage drops (rises) to -4.35V. With just the U1 connected it is something around -4.75V.
Additionally, when I hit strings any harder than just touching them the signal gets overdriven as heck, and ADCs readings drop to 0.
Totally stuck at this one. Every idea will be appreciated.
You can see my little monster here
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5 years 4 months ago #1578
by Ray
Replied by Ray on topic Input stage problems
Hi, wow! congrats for that monster 
a true piece of hard work!
By what you mention, seems that your DAC works fine, so you should focus on the ADC area,
To make sure that the ADCs work fine, you can try an experiment like this:
www.arduino.cc/en/Tutorial/AnalogInput
Just using a potentiometer and the serial port you can read the values.
The input stage is pretty simple, make sure that your op-amps have the correct supply and the resistors are placed correctly, 90% of the times is a silly mistake.
Let me know about your progress!
a true piece of hard work!
It's not a problem using an LMC7660, just make sure that you get +5V and -5V out of it.I changed are LMC7660 instead of TC1044 and 1N5818 diodes instead of 1N5817. Both 1044 and 5817 were impossible to get somewhere around.
That is normal.With just the U1 connected it is something around -4.75V.
That's fine.1N5818 diodes instead of 1N5817
By what you mention, seems that your DAC works fine, so you should focus on the ADC area,
To make sure that the ADCs work fine, you can try an experiment like this:
www.arduino.cc/en/Tutorial/AnalogInput
Just using a potentiometer and the serial port you can read the values.
The input stage is pretty simple, make sure that your op-amps have the correct supply and the resistors are placed correctly, 90% of the times is a silly mistake.
Let me know about your progress!
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5 years 4 months ago #1580
by carminacore
Replied by carminacore on topic Input stage problems
First of all, thank you for your time, Ray!
I did check my ADC with the simple potentiometer. It seems fine, I can sweep through the whole range 0-1023.
Can you please tell me what typical range of the ADC readings should be?
Going to check all the connections once again.
I did check my ADC with the simple potentiometer. It seems fine, I can sweep through the whole range 0-1023.
Can you please tell me what typical range of the ADC readings should be?
Going to check all the connections once again.
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5 years 4 months ago - 5 years 4 months ago #1581
by carminacore
5 years 4 months ago #1582
by Ray
Replied by Ray on topic Input stage problems
Hi,
Let's fix one thing at a time!
Make sure also that the op-amp is powered with -5V and +5V.
The causes for this low 0.1V on pin3 could be:
- are you using tl072 op amps or are you using other flavors?
- measure R19 & R20 voltage divider (www.electrosmash.com/images/tech/pedalsh...shield-schematic.png) and make sure that you have 1.66V there. Then measure across the R2 and R3 resistors and check where the voltage disappears. Lowering R2 to 1M could help...
Let's fix one thing at a time!
This is wrong, pin3 should be something around 1V (0.9measured on my board) and pin5 should be 1.6V.I still get like 0.1-0.2V on U1 pin3.
Make sure also that the op-amp is powered with -5V and +5V.
The causes for this low 0.1V on pin3 could be:
- are you using tl072 op amps or are you using other flavors?
- measure R19 & R20 voltage divider (www.electrosmash.com/images/tech/pedalsh...shield-schematic.png) and make sure that you have 1.66V there. Then measure across the R2 and R3 resistors and check where the voltage disappears. Lowering R2 to 1M could help...
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