Voltage drop - Githubissues

jvoermans commented 3 years ago

@jerabaul29 , connected the 3-axis geophone today, works great! :)

I have a hardware issue though, which is a voltage drop across the amplifiers (INA122). As you know, I have 5 of them in parallel. Is it because of all the resistors? Rather than 3.3V, there is 2.9V now. Not a direct issue in the functioning of the instrument, but it also means that the readable range of vibrations is not 0-3.3V but 0-2.9V, thus loosing a bit of bandwidth here. INA122s

Any suggestions? Can we get rid of some of these resistors somehow?

jerabaul29 commented 3 years ago

I will have a look / thought at this. Can you post again the image of the full setup? :) .

jerabaul29 commented 3 years ago

I think there are a few things that are a bit strange:

if I read the drawing correctly the upper resistors (ie the row of resistors that is highest up) are short-circuited. So they basically do nothing. Is that expected?
you use the LM358, right? This is well this chip:

https://protosupplies.com/product/dual-op-amp-lm358/

The wiring you have does not seem to correspond to what is described there (for power in / out etc). Are you sure that the drawing you show is correct / corresponds to what you have actually built?

what is the point of the resistors between the +5V and the GND?

The kind of drawings you show are very convenient for showing things to beginners but are not very convenient for discussing slightly complex circuits, could you consider drawing this in KiCAD EEschema if you plan to use kicad anyways, that would be a good exercise and will make it easier to discuss :) .

Regarding the power drop: you now have 5 x 220 ohm resistors between the 3.3V and the GND, ie a drawing of 75mA. This is probably in addition to the drawing of the GPS, SD card, geoduinos, etc. This may be a bit much drawing from the 3.3V pin, and may lead to the voltage reduction. I think that when we use a PCB with "native" 3.3V supply the problem should disappear.

jerabaul29 commented 3 years ago

Ah no wait now I understand, I was reading it wrongly, the first row is not short circuited. It is a bit tricky to read these drawings, Eeschema will be easier :) .

jerabaul29 commented 3 years ago

(I still have a problem understanding how you provide VCC to pin 1).

jerabaul29 commented 3 years ago

I wonder if I have the right datasheet for your component. Can you send me the link to your ampop datasheet?

jerabaul29 commented 3 years ago

(just for myself for reference, should use the amplifier circuits http://webpages.ursinus.edu/lriley/ref/circuits/node5.html ).

jvoermans commented 3 years ago

Sorry sorry, forgot to mention I use a INA122 amplifier. I didn't change the name in the Fritzing sketch! ina122.pdf

I'll attempt this weekend on working in KiCad :)

jerabaul29 commented 3 years ago

Ah, that explains :) Then everything makes sense. I just think that the lower voltage is due to the current drawn, should be fixed in the final logger when having a strong 3.3V supply on the 3.3V line. It is late though, will double check tomorrow morning :) .

jerabaul29 commented 3 years ago

Should be fine I think. Closing.

jvoermans / Vibration_Logger

Voltage drop #18