Reading Surf Pi 1.2 Output on Raspberry Pi

[Amphibot]

Hello,

I'm working on a design project in school. We were hoping to connect our Surf Pi 1.2, which we have up and running, to a sort of remote controlled car we built. However, we would like the audio signal from the piezo buzzer to instead be sent to the Raspberry Pi through the GPIO pins. Is this possible? Would anyone be able to help me figure out exactly what type of code I would need to be writing to do this, and whether the buzzer signal is compatible with the GPIO pins on the Pi in the first place?

Thank you in advance for any help you can offer!

[Skippy]

Many people would advise you to use an opto-isolator, to keep the detector circuitry seperate from the Raspberry. Example: use linear optocouplers like the TIL300 (IL300 etc) to pass the analogue signal across. If you just want simple 'beep or not' information transfer, a plain opto-isolator will suffice. Drive the LED from Q6 collector to +12 V supply via a suitable resistor.
If you're prepared to join the circuits directly, remove the volume control pot, replace with a fixed resistor from collector to +5 Volts, and measure the collector voltage of Q6. If your PI can only measure 3.3 V max, you'll need to make a divider up. Eg. 1k0 from Q6 collector to +5V, 2K0 from collector to 0V ground. Measure the collector voltage, as before.

[Amphibot]

I've never made an opto-isolator, but it makes sense as far as transferring the signal. I still wonder how I would then read the information from the Raspberry Pi. Would I need a DAC to be able to read the signal? I know it doesn't have an audio input, but I wondered if there was a way to input the signal using the GPIO pins?

[Qiaozhi]

Hello,

I'm working on a design project in school. We were hoping to connect our Surf Pi 1.2, which we have up and running, to a sort of remote controlled car we built. However, we would like the audio signal from the piezo buzzer to instead be sent to the Raspberry Pi through the GPIO pins. Is this possible? Would anyone be able to help me figure out exactly what type of code I would need to be writing to do this, and whether the buzzer signal is compatible with the GPIO pins on the Pi in the first place?

Thank you in advance for any help you can offer!

I have not had the opportunity (or the time) to look at the Raspberry PI, but I think this is what you're looking for ->
https://www.raspberrypi.org/documentation/usage/gpio/

[bernte_one]

here is something that helps me for arduino
http://www.designer2k2.at/mods/ardui...-io-protection

[Skippy]

It appears there is NO analogue input on the Raspberry, which surprised me. This article may help:
http://www.raspberrypi-spy.co.uk/201...ng-an-mcp3008/

[Skippy]

I've thought some more about this. The purpose of the analogue switch U7d is to chop the drive to transistor Q6, so it produces an audio tone. The Raspberry doesn't need this, it wants the unchopped signal from the opamp U3a output. This is a positive-going signal, related in strength to the detected signal, and would be the best signal to feed into a TIL300 based opto isolator. Have a look on TI's website, there's plenty of data on this part, application notes, etc.
Another alternative approach would be to have the analogue output of U3a control a "voltage-to-frequency" converter. This is basically an oscillator, whose running frequency is influenced by an applied control voltage. You can get dedicated IC's that do it, or there's NE555-based circuits, or the cheap CD4046 phase-locked loop chip. The output of this oscillator could then be fed to a plain photo-transistor opto-isolator. The photo-transistor output could then simply feed a digital (ie. 3.3 Volts / 0 Volts) signal direct into the Raspberry IO port, all that's needed is a single pull-up resistor to 3.3V. Then it's a software timing issue to extract the info from the pulses. This shouldn't be too hard, it's a standard technique, there's very likely to be some example library routines online. Many sensors are interfaced to digital inputs this way - variable frequency or variable pulse-width. All avoid the need for analogue-to-digital converters.