#intertec

Kermit and the Brain

It’s the mid 1980s.  You have a file want to transfer from one computer to another, but these machines are vastly different.  Both have RS-232 serial.  That might help, but you have no common protocol to transfer that file.

A frog comes to your rescue.

Seriously though, the Kermit file transfer protocol is one of the most widely ported piece of software out there -- and for good reason.  Douglas Crawford explored the ubiquitous transfer protocol on two CP/M capable machines, and an IBM PS/2 luggable running MS-DOS.  The Kaypro II machine is plenty common, but the Intertec Superbrain (another Z-80 based machine which ran CP/M) is a recently restored gem.  Douglas demonstrated the compile time of the 8080 build of Kermit on his Superbrain, which didn’t take much time at all.  Then he transferred some files from the IBM over to the Superbrain like it was nothing.  The best part i that Kermit is still a viable data transfer method today when moving information to and from legacy machines.

At first sight

The power supply is based on the MP023 chip. It is a one-cycle DC-DC controller created by Monolithic Power Systems in 2016.

Schematic: Input → filter → bridge rectifier  → flyback converter with rectifier working for the output C-filter.

From the converter output, the voltage comes to the PWM modulator unit based on the Silicon Labs EFR32 "Wireless Gecko" module.

Luminaires are connected to the modulator output via the output connector.

The marking on the power supply case: λ>0.8, and the coefficient value hints at a passive corrector.

The radio elements are assembled neatly. The circuit board has no electrical defects, and the connection quality is good everywhere.

Test results

• The pulsation value as a fraction means that the voltage has pronounced HF (numerator) and LF (denominator) components.

• The hottest component in the power supply is the output rectifier diode. The measurement is taken with the cover removed.

• The overcurrent protection is triggered at an output current of 1.3A, first limiting the current; then, when the voltage drops to 17 V, it goes into start-stop mode.

Output voltage pulsations

Slow sweep waveforms

Fast sweep waveforms

Conclusions

• This power supply has a high level of output voltage ripple. If it were not for the built-in wireless control module, this power supply would be trashed. BTW, if you want to reprogram the wireless control module, check out the articles here (in new tab) and here (in new tab).

• The element heating at full load and with the cover off is 154 F, which gives some reserve.