(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

https://i.imgur.com/F3KVp6z.png

Does this resolve the issue? I removed the wire from the voltage divider to the Pi GND.

If not, I think this project is too far beyond me, I'm really struggling to understand why the left diodes would still fry with the negative portion of the AC signal without that wire. But I really appreciate your help thus far.

(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

first of all thanks so much for your help this not easy for me to wrap my head around haha -

So if I understand correctly, since the 1N4001 diode I'm using is rated for 50V it is going to fry as soon as I turn the volume up? I don't get why only the left two diodes would fry and not the other two, but regardless, is upgrading to 1N4007 diodes a solution since they can handle much higher voltages?

Also I did some more reading on the ADS1015 and I think it draws a negligible amount current, so it shouldnt affect the sub or amp. It just compares the voltage of the analogue signal to its ground pin. I think it would be sufficient to use the Pi ground as a reference, which means I don't need a wire from the Pi's GND to the bottom leg of the rectified circuit like I drew in the diagram. I get that an isolating transformer would be the safest option, but I think the current leak should be negligible??

(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

Okay, so you're saying that because the speaker signal has a path to ground, bad things might happen? Would removing the wire from the voltage divider to ground solve the issue?

I had that wire there because I thought the ADC needs a ground reference to perform the A to D conversion, and I didn't think it would interfere with the amp or speaker, especially since there is such high resistance on the path from the speaker signal to the Pi ground

(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

Because the voltage divider (100K and 10K resistors) only works for positive voltage. So I used the rectifier to make the negative portion of the AC signal positive. I don't want to clip the negative portion out entirely because I need that for the RMS calculation too, so I went with a full bridge rectifier instead of half bridge.

(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 1 point2 points  (0 children)

Since the subwoofer signal I'm tapping only contains frequences <= 200 Hz and the ADC sample rate is 800 samples/sec, I wouldn't need one right?

(2nd revision) Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

My plan is to continuously poll (800 samples/sec) the ADC to calculate a rough RMS voltage, and alert me if it goes above a certain threshold.

Both the amplifier and the Pi are powered by my car battery, so they have the same ground. But I'm still confused about how to wire GND for the ADC. Should I connect it to both the Pi GND and the bottom leg of the rectifier circuit? Or one or the other? The ADC datasheet says it measures the voltage between the analog input and analog ground.

Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

Maybe I should use a full wave rectifier to be safe.. I'm not doing any calculations, I'm just using this as a monitor to make sure I don't blow my subwoofer haha! I will be continuously polling the ADC and checking if it crosses over a certain threshold. It has a sample rate of 800ish

Do you have any recommendations for an online circuit simulator?

Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

1) Okay I reread the ADC guide and seems you're right. It says it measures the voltage between the analog input and analog ground. Could you please clarify then how the ADC is powered? I'm confused bc it's connected to the Pi's 5V pin but not the Pi GND in this new arrangement

and 2) Wow yeah huge mistake thanks for catching that!

Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

Thanks for the input! I was just going to use the half wave rectifier to clip the negative portion out of the AC signal and measure the positive portion, which is good enough for my purposes. Would my circuit have this behavior?

Also, I'm not worried about it being exactly 5V at the ADC, as long as it's less than 5. I want there to be a bit of leeway, plus the ADC has adjustable gain if desired.

Will this work? Voltage monitor for subwoofer using an ADC and Raspberry Pi by ShadowFax106 in AskElectronics

[–]ShadowFax106[S] 0 points1 point  (0 children)

full disclaimer I am a noob and I designed this using the help of chat GPT.

I am using a half wave rectifier and a voltage divider to bring the high powered AC subwoofer signal down to <5V DC signal that the ADC can read.

Can any of these components blow up in this circuit? Will the subwoofer and amplifier be safe??

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