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Topic: ADSR Envelope circuit breaks power module on Nano (Read 191 times) previous topic - next topic

NardJ

Apr 12, 2019, 06:47 pm Last Edit: Apr 13, 2019, 09:12 am by NardJ Reason: Updated circuit (pwr-in missing, chip Vss connection connected to wrong rail
Hi, I am making a module for a DIY modular synthesizer. The module applies an ADSR-envelope to an audio signal using a 10K MPC41010 digital potentiometer.

I suspect, I made an error in the circuit, since I now have 2 Nano's which will not power on from USB (pwr led flashes a few times and then stays off). Attached you find the circuit and the pinout of the MCP41010.

The second Nano I tried without audio-in/audio-out/gate cables attached, so I know it is not the audio signal causing this. Am I doing wrong in the circuit (sinking too much power perhaps)?





Any help is much appreciated!

MarkT

Start with fixing the misconnected V+ on that chip, and add a decoupling capacitor for the chip.

Then find the short circuit using a multimeter in beep mode perhaps - sounds like you've a short
somewhere.

Then you'll need to consider the fact that digital pots cannot handle a signal outside their
supply range, which is going to be a problem with an audio signal biased around 0V.

Then you'll need to accept the fact a 256 step pot will give audible artifacts as it changes value.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

NardJ

Hi MarkT, thx for your reply!

Do you mean the Vss and Vdd on the MCP41010 are swapped? (I have Vss connected to ground and Vdd to 5V) or ...
the 5V of the chip which I connected in the drawing to the lower GND rail? (In reality this was connected to 5V rail, made a drawing mistake.) I fixed to drawing.

Which capacitor should I use? 100 nF?

I do not understand what you by "digital pots cannot handle a signal outside their supply range". The audio signal I generate and use a input for this circuit has a range from 0 to 5V.

cheers, Nard

Grumpy_Mike

#3
Apr 13, 2019, 11:26 am Last Edit: Apr 13, 2019, 11:29 am by Grumpy_Mike
Quote
I do not understand what you by "digital pots cannot handle a signal outside their supply range"
The chip is powered by a 5V supply referenced to ground. So any signal you apply to it must be above 0V and below 5V.

Quote
The audio signal I generate and use a input for this circuit has a range from 0 to 5V.
Has it?
If this is so, and it is highly unusual, then you are shorting the DC bias on that signal to ground with your ground connection on the Audio Input socket.

Audio signals go above and below their DC reference point, so a voltage range from 0 to 5V should have a DC reference point at 2.5V. This is the point you are connecting to your Arduino's ground.
If your Audio signal that you apply to this is totally isolated from your Arduino's power supply then you will be applying negitave voltages to the chip's input, which will damage it. If it is not an isolated supply you will be damaging your audio signal generator and could damage that.

The key to fixing this is to AC couple the audio into the chip. ( using a series capacitor ) and then add a DC bias to the input of the chip with a 10K pull up and a 10K pull down on the input. It would be good to also AC couple the output of that chip to the output socket.

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