Friday, August 3, 2018

Wrapping up and transporting teletypes to CHM for the Vintage Computer Festival West


Last night I performed my first tests of the new circuit and modification that would allow the SBC 6120 (PDP 8 clone) drive the ASR 33 teletype using the Reader Run Control feature which throttles the paper tape reader to protect against overruns. 

The test did not work properly. Some portions are working, but the small relay board was not turning on and off in sync with the Data Ready bit of the Harris 6402 UART chip on the PDP 8 clone. I picked off that signal and brought it out to a 74HC04 inverter chip, then routed it to an Arduino type relay board that will switch the 12V to the teletype control feature.

I realized that I had powered the new circuit and relay board from a separate power supply, but had no tie of the ground between the SBC 6120 and the inverter chip circuit. Can't respond without a complete circuit for electron flow. The fix would be to power the relay board and inverter from the 5V supply on the SBC 6120.

I am not sure if I will have time to make the changes and test again. Likely this will be done after the end of VCF West. I still have to write up some support material for my booth helpers and begin to collect and pack everything for transport this afternoon. 

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