Saturday, October 18, 2014

Disk drive timer finished and installed, SAC interface circuits built, and debugging underway of the keypunch interface


I finished assembling the timer neatly into a plastic project box, with appropriate air holes to dissipate  the heat produced by the zener diodes, voltage regulator and relay timer board. One final test validated correct operation - roughly 105 seconds after the motor is switched on, the heads load when the timer circuit activates. It is now installed and the disk drive enclosure put together.

Timer circuit in its enclosure

Timer box in its final location

Everything closed up, front door in place


When I retrieved my power brick and powered the Arduino, it showed some pathology without being hooked to anything. Periodically, the Arduino would reset and start over, which I suspect is a power protection reset due to excessive draw by two relay boards fed from the Arduino.

I think I can take the 5V from the brick input and bypass the rest of the Arduino circuitry that is overloaded, although I might need to add my own 5V regulator on the power if I see any signs of sensitivity to power variations. I have to sort his out, but by removing the connection of +5 from Arduino to the relays and connectors, I can resume testing some logic for now.

I cleaned up code for quite a while with the 5V disconnected, but when I tried to open the user serial link to get into more serious debugging, it was clear that the serial port card I use also requires 5V. I had to separate out the connections from those for the power hungry relay boards and connect it individually before I could begin talking to the Arduino.

Next minor snag - the interface box has a male DB9 connector and the only USB-serial adapters I have also have a male DB9 connector. I found a female-female adapter but when I began testing it was clear that it was not a crossover inside. I need to have a crossover adapter or cable with female connectors on both ends.

The power brick for the Arduino is 12V, which is dropped to 5V by an onboard voltage regulator, so I will need to wire up a voltage regulator in order to feed the relay boards bypassing the Arduino onboard power system. I have the parts and began to build it, while ordering the DB9 adapter I need to continue testing.

Discovered that the relay board activates a relay on logic low input, not high. Reversed my logic and all was well. I changed the code controlling the relay signals to use an indirect value - PICK or DROP - rather than LOW and HIGH due to the potential for confusion because of inverted activation.

Set up the voltage regulator and an external 12V 4A power brick. Now that I have the right adapter and power to the system, I am still not seeing output from the user serial port nor getting any input into the system.


I breadboarded my receiver and driver designs for the SAC interface, but will postpone testing until tomorrow. I have to set up +3 and +6V power, some TTL driver and receivers, and then wire it into the SAC adapter for testing. I want to move carefully to avoid damaging the 1131. I will pick an interrupt request line as my driven signal and the corresponding int level active line as the received one - an easy pair to test with that don't require any other signals to be connected.

My board has twisted wires, similar to the twisted pair used in the IBM signal cables. My bench power supplies will deliver the SLT voltage levels and a digital trainer unit I have offers TTL level inputs and outputs. When all set up, I should be able to flip a switch, step the 1130 to have it enter an interrupt routine, and see the indicator lamp light reflecting the entry.

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