Using a Pi Pico to send-receive IC-V data to Icom transceivers

Pi Pico used to send CI-V data (with 7417 TTL buffer) to IC7300 or IC9700 Radio

Radio	Addresss (hex)
IC7300 MK I	94
IC7300 MK II	B6
IC9700	A2

A Pi Pico can't be connected directly to your Icom transceiver via the CI-V line at the back of the radio - we need an interface. The CI-V line is two-way having data going from the Pi Pico to the radio as well as data going from the radio to the Pi Pico (but not at the same time of course). Ideally we need an interface that will i) cope with the voltage difference between the Pi Pico and the radio, ii) not stop data being sent from the radio when the Pi Pico is idle, iii) can split the Tx and Rx signals to go seperate Pi Pico GP pins and iv) cope with the correct baud rate speed etc.

The Pi Pico UART idles high (3V) and data is sent when it drops to 'zero'. ChatGPT suggested various interfaces to go from the Pi Pico to the Icom radio but many were simply a single transistor inverter. Not only will this invert the UART data but when it idles high it will essentialy ground the CI-V line stopping other traffic being able to be sent along the IC-V.

I tried a few interfaces but this one using a 7417 buffer (from W8WWV's Icom interface, see link below) has worked with the Pi Pico projects perfectly.
Note: R1 is a little low in value, I guess he used this to get maximum speed. but as we are using a relatively low 19200 baud rate R1 could probably could be raised to 1k or even perhaps 4k7
- it's experimental and a higher value might be safer for your rig (you could also try adding a 100R in series with the CI-V output to the radio).

Note I: as the interface input is connected to it's output, you will receive back into the UART buffer everything you send out. So in the code remember to delete the buffer immediatly after sending out data to the radio (or at least compensate for this - the UART buffer is not very large on the Pi Pico).

Note II: once you set-up the UART in the software, it will receive even if your code is not using it, so the buffer can easily fill up with CI-V traffic from the radio.

In the S-meter project I have sent out the S-meter data value as a pulse width modulated (PWM) signal on GP16. You need a simple low pass filter (LPF) to 'average' this into a DC signal which you can send to a data logger (see circuit above). It would be a good idea to have a unity gain (op amp) buffer between the output of the LPF and the data logger. The micro python used on the Pi Pico has a built-in file system which can create comma seperated veriable (CSV) files, and so I am also working on building this into the S-meter project (more soon).

When you request an S-meter reading via CI-V, the frames that come back are often delayed (sometimes by many seconds) further more the value that comes back may not mirror exactly the value shown on the front panel meter. Its seems the S-meter value sent back via CI-V is an average of the meter readings. S0 to S9 +60dB comes back as 'vales' of 0-255 in binary coded decimal. So in principle S0 will give back '0', S9 gives about "120" and S9 + 60 dB will give '255'. The value comes back in two bytes in the S-meter request CI-V frames. So in the S9 + 60dB case i.e. '255': one byte will contain '2' and the other '55'. If you multiply the '2' (hex) x 100 and add it to the '55' (hex) you will get the full value of 255 (decimal). The numbers might be hex but A - F are never sent, only binary coded decimal are actually ever sent.

Note: The S-meter value (0-255) sent back along the CI-V frames is not linear with the S-meter reading (it may not be 6dB per S-unit either). There are semi-accurate formula (e.g. dB above S9 = (raw-120)/3, see my code) that will convert the raw value into an equivalent S-meter value but they are very rough. You could use a look-up table etc. Either way, with this prototype set-up you can at least log a beacon or station and see how the signal is improving or diminishing over time. You could either calibrate the raw values coming back using the front panel meter reading or better still measure the raw values against a know calibrated signal source etc.