Breadboarding and testing on the air

The next iteration was to put the chip on a breadboard and add other required components and an optocoupler for interfacing with the radio.

The operating voltage of the MSP430 chip is somewhere between 1.8-3.6V (according to a datasheet). So 2 AA batteries in series would be enough. Also, it needs to have a positive polarity via a 47kOm resistor on the RST pin (up). Otherwise, the chip won’t start. Also, a small ceramic capacitor (100pf or so) is recommended across the power pins.

The minimum working configuration on the breadboard has a chip, 47k resistor, a tiny capacitor, and some LEDs. I couldn’t find a 47kOm resistor in my junkbox so I substituted it with 2x22kOm resistors in series.

The next step was adding a 4N36 optocoupler in series with the green LED – this will key the radio. The plus wire goes to pin 1 and the pin 2 is connected to the negative power bus. The collector and base of the optocoupler are connected to the key:

Polarity and current are crucial. I tested polarity and current on the CW key contacts before connecting the optocoupler. The current was about 1mA only and the plus (positive) wire goes to collector (pin 5) and reference (ground) goes to emitter (pin 4).

The total budget for the project so far is $7.30 ($4.30 for the msp430 chip and the development board, $1 for breadboard, $1 for LEDs, $1 for optocoupler; resistors and capacitor have been salvaged from an old computer power supply).

Quick test on air and bingo – we have been spotted by DR1A:

Isn’t that fun?

The next step will be to make this somewhat permanent and add an enclosure – most likely some plastic food container.



About va3paw
Ham radio enthusiast, software developer

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