How to Turn Your PDP-12 Into a Crappy Theremin

By -

There's a demo / video I've been meaning to record for a while, showing how a simple punch-in program and deft use of the auto restart feature can turn the PDP-12 into a musical instrument, thanks to the PDP-12's speaker (which clicks when the MSB of the AC changes state). Click "read more" to watch the video!





Comments

Post a Comment

Popular posts from this blog

Power Supply: The Mystery Continues

By Anonymous -
Image
I continued testing the power supply. It would work most of the time it was powered on and give the correct voltages, but then sometimes when it was powered it the +5V circuit breaker would trip. I managed to capture this on the oscilloscope The peak voltage was 5.16V and then the breaker trips and it goes down to around 1V.  Time to keep investigating the G824 module to see if there is something wrong with it. (Michael from RICM has been very helpful with troubleshooting so far).  I borrowed a nice mixed signal scope from the EE shop. It blows my HP 54200A out of the water. The +5V regulator is supplied by the +8V line. So Michael suggested looking at both of the lines as they power on to see what they look like. Not Tripped Tripped Above are the results of this. I measured the peak voltages for both lines when they tripped and didn't trip. The +5V line averaged around 6.6V when it didn't trip and averaged around 12V when it did trip. The...
Read more

Serial and Other Diagnostics

By Anonymous -
Image
Warren came up from South Dakota to help us get the serial ports working and do some more diagnostics. Sunday night he made a cable to connect the serial card to the serial port on our computer tower. We are using Warrens modified copy of MTTTY (Multi Threaded TTY) as our TTY emulator. It is an old Windows program so we are running it in Wine and it has been working pretty well so far.  After On Monday... We toggled in two simple programs. One was a send/receive program and the other was a send. The send would take the data input on the right switches and display the character or number associated with that number in MTTTY on the PC. The code for that is as follows: 0200 / 7604  LAS 0201 / 6046  TLS 0202 / 6041  TSF 0203 / 5202  JMP 0204 / 5200  JMP  The LAS instruction loads the AC with the switch register. TLS Sends the AC to the serial port. TSF will skip the next line if the flag is set. JMP will jump to 202 and then the next JM...
Read more

Power Supply: Fixed

By Anonymous -
Image
Testing continued on the power supply. I borrowed a few 4Ω 255W resistors from the Power Systems lab so I could try and load test the supply.      With four of these resistors wired in parallel we get 1Ω. Because of Ohms law this means we will get a 5A current from the 5V output. This would give about 25W of power, (P=V*I). 900W is more than enough to satisfy this. The result of having the load was a drop in the output voltage. The 5V line dropped from its normal 5.07V to around 4.96V. I hooked the oscilloscope back up to measure the +8V and +5V lines as they power up. Compared to before this was a much better graph. There is a much lower spike in the +5V output, it jumps to 5.8V and then quickly settles down to 4.8V to 4.9V (according to my multimeter). The power supply appears to be working just fine now. No more random tripping and no more burning resistors. Next on the agenda: Powering up the machine and running a few basic tests. Posting a lis...
Read more