Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
10 years, 11 months ago.
Time Division Multipexing: Using one channel to read different signals
Hi,
I want to sample around 3 or more signals using one channel of the MBED ADC. I know that it has 8-channels, want to try this approach, I am using an analog mux to send the signals (sine of 25, 100 and 150 Hz), the circuitry is working fine, but when I recover the signals I am getting a different frequency altogether on all three (300 Hz). Anybody has tried this approach?
Regards, Manas
1 Answer
10 years, 11 months ago.
I don't think it is the most straightforward solution, if you would lack analog inputs I would probably just use a standalone ADC IC instead of an analog mux IC, but it should work.
One possible problem would also be that the LPC's don't accept much capacitance at their input, so that can cause issues. But which code are you using? If you get 300Hz on all three outputs I would guess something goes wrong with your multiplexing/demultiplexing.
Hi, the mux works fine, cross-checked on an oscilloscope, has anybody attempted this before? For eg. there is a good discussion on noise effects here! Anything like that on multiplexing and using a single channel of the ADC of MBED kit
posted by 19 May 2013I am sure your mux works fine, but I don't think the combination of your mux and demux (in your code) works fine. The noise effects will be the same as when you use multiple channels of the mbed, since then you are also still using a single physical ADC, only you are using a different mux. But noise cannot transform a 25Hz signal into a 300Hz signal.
I can summarize the noise effects: 1/f noise will be a bit correlated between the channels. But that is exactly the same as what you always have since in normal operation there is also a mux doing its job.
posted by 19 May 2013