I2S microphone (ICS43434) to a Teensy 4.0 with cable? Length + type?

[AlainD]

Hi

I'm thinking of connecting a I2S microphone (ICS43434) to a Teensy 4.0 with a cable.

I know it's designed for pcb - pcb connections, but what is possible lengthwise?

Does the cable makes a difference?

 

[MarkT]

30cm? 50cm?

You can pull various tricks for longer distances over cables, like series resistors to reduce overshoot and the risk of reflections, but I2S is pretty vulnerable due to most of the signals being clocks (double-clocking due to waveform distortion is a common issue). Good ground-return is essential, and EMC can be an issue.

Personally I'd favour using a twisted pair to ground for each I2S signal, with the load-end having a 270R:270R bias network which partially terminates and imposes lower current demands on the driving end than a single pullup. The driving end still needs to be able to source/sink 10mA or so per signal which this at 3.3V, but it will allow the signal to travel a lot further, being a roughly-matched transmission line. CAT5 cable can be used.

 

[AlainD]

Hi

I did a search on a "270R:270R bias network", but didn't find info that was relevant and understandable for me. Can you give a sketch?

 

[MarkT]

Something like this:

The source sees about 120 ohms, but centre-biased, so that at 3.3V supply it only has to drive about +/-12mA, not 25mA
This terminates the line well enough that reflections are not a problem. Its an old trick that saves current and power too of course, constant 20mW rather than an average of 40mW (worst case 80mW) with a single 130 ohm pullup or pulldown. And less EMC issues too.

You could use 240R for a 120R line, but 270R presents a good enough match and reduces current and power. It should work well enough for even a 100R line.

Twisted pair lines are typically in the 100 to 120R impedance range.

 

[AlainD]

thanks, very clear now.

 

[DD4WH]

I have successfully used the ICS43434 and Teensy 3.6 with simple cables of about 8cm, see here:

Hardware setup

Environmental Sound Recorder for Teensy 3.6. Contribute to WMXZ-EU/microSoundRecorder development by creating an account on GitHub.

github.com

 

[AlainD]

I have successfully used the ICS43434 and Teensy 3.6 with simple cables of about 8cm, see here:

Hardware setup

Environmental Sound Recorder for Teensy 3.6. Contribute to WMXZ-EU/microSoundRecorder development by creating an account on GitHub.

github.com

Are you sure about the 1000 ohm? :
"use an RC lowpass filter (100µF electrolytic cap to GND, 1000 Ohm series resistor) to filter the 3.3V line from the Teensy before connecting it to the 3.3 Volts line of the ICS43434 PCB"

 

[DD4WH]

Yes. Why not try it by yourself? It worked for me.

If you are too shy, try something like 100 Ohm instead.

 

[AlainD]

Yes. Why not try it by yourself? It worked for me.

If you are too shy, try something like 100 Ohm instead.

You lost me. The 3.3V is a power supply and -hopefully- mostly DC. A 1000 Ohm or 100 Ohm resistance on a power supply (for the mic) doesn't seems to be a good idea to me.

 

[h4yn0nnym0u5e]

That “mostly“ is the point - the RC network filters noise out of the supply, which is pretty noisy as it’s powering the processor. The mic takes about 0.5mA according to the data sheet, so 1k drops the 3.3V down to about 2.8V, well within the acceptable range.

 

[AlainD]

That “mostly“ is the point - the RC network filters noise out of the supply, which is pretty noisy as it’s powering the processor. The mic takes about 0.5mA according to the data sheet, so 1k drops the 3.3V down to about 2.8V, well within the acceptable range.

Thanks.

 

[MarkT]

I'd suggest using 1000+ ohm ferrite, and say 10 ohm resistor, then the mic can have less supply droop and good filtering?

 

[Cuble1998]

I also suggest to use some premium and flagship microphone for better recording.

 

[DD4WH]

@Cuble1998
I think you are a bot, do you agree?
If not, please be much more specific in your recommendation