Multiple External Potentiometers
Thread Summary
The user is trying to use 7 external potentiometers with a DSP that has only 4 DACs. The support engineer suggests using a quad analog bilateral switch driven by a GPIO output to multiplex the pots, and provides an example project for the ADAU1701. Another approach is to multiplex 8 pots into one AUXADC input, which can be scaled to 32 pots if using all 4 AUXADC inputs, though this may be limited by the DSP's MIPS. The user considers adding another ADAU1701 DSP board to increase available MIPS and DACs.AI Generated Content
I understand this DSP only has Four DACs, so I can only use 4 potentiometers in my SigmaStudio project. I am trying to use total of 7 external potentiometers to manipulate the audio coming in. Any suggestions on how I can achieve this? Is it even possible?
Any input would be greatly appreciated.
Thanks.
external
Audio Signal Processors
potentiometers
hardware
apm2
SigmaDSP Audio Processors
adau1701
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Hello Jendo,
This topic is somewhat tricky. Yes, it is certainly possible to do this. There are a lot of hardware details and there are some pitfalls that could come into play.
One of them is capacitance. Think of the situation of switching between two pots with one that happens to be set at max setting and the other at minimum setting. This means that one of them is sitting at ~3.3V and the other ~0V. When you switch between them the capacitor (either stray or real) has to charge or discharge. At that point the signal is available to control the volume control or whatever it is controlling will see this charging or discharging. Plus, you have to "hold" the current setting while the other pot is selected. Therefore, it is wise to sample this setting at certain times once the data is settled.
The drive impedance of the external circuit also comes into play with how fast it will charge this capacitance and remember that the AUXADC is a switched capacitor type of ADC. I am saying all this so you know what to look for to see if you are having problems.
I have two example projects to get you started. The project is somewhat complex because they both use oscillators creatively to develop the switching signal and to develop a small window to hold the data only after it has had time to settle after switching. So it does not make the new selected pot active right away. There are things in this project that can be removed and were only used for verification that it worked.
This first one uses only one GPIO output that would drive one quad analog bilateral switch to have four switches thar switch between two different pots. So this would allow eight pots to feed the four AUXADC inputs.
ADAU1701 AUXADC External MUX Example.dspproj
The second project is even more adventurous. It multiplexes eight pots into one AUXADC input. If you did this for all four AUXADC inputs then you would end up with 32 pots!! However, the limited MIPS with the 1701 would be limiting the application. These techniques could certainly be ported over to the ADAU!452 and that processor is so much more powerful.
4478.ADAU1701 AUXADC External MUX Example 8 to 1.dspproj
Enjoy!!
Dave T
Dave,
I just realized this recently. I ran out of MIPS in my current program, which sounds very well using my component speakers and my subwoofer. Therefore, I'm not able to use the DACs to manipulate the sound, so I thought, why not just buy an additional ADAU1701 DSP board? This would allow me to split my current program and hopefully give me enough MIPS to use potentially EIGHT DACs!!! =)
Thoughts?
Hello Jendo,
Yes! For sure!!!
I have worked out a design a year or more ago using several ADAU1701 DSPs and one ADAU1452. I used the 1701s as sort of like GPIO expanders and also used the converters for more inputs and outputs. I also used some of the I2S comms ports to not only transport the audio but also some logic and the AUX ADC signals.
I have not had time to finish this design so I do not have a good example to send over. It was a personal project (yes, I love this stuff so much that I do it on my own time for fun!)
Do you think your program might be able to be trimmed down a little to make it more efficient? However, if you want to do more processing then going to multiple DSPs is a valid solution.
Dave T
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