It appears that my progress on my Monotype computer interface is so slow that parts obsolescence is catching up with me.
A few months ago I was looking into future supply of parts for the interface and found that the UDN2987 IC’s I was using had been discontinued by the manufacturer and were no longer available. These convert the individual air line signals from the low-power digital outputs of the microcontroller to high-current sources that can activate the solenoid pneumatic valves. There was nothing else with similar functionality (8 logic inputs driving 8 high-current loads) available either. All the new high-current drivers either use a custom single-bit interface to control them or use I²C (a standard for communications between digital components). This would ultimately simplify the circuit because these can all be chained and so use only one digital output on the microcontroller , whereas the current circuit needs 31 digital outputs, one for each air signal. But is still requires changing the circuit and PCB layout.
Just this week, I received a notification that the NXP LPC1343 microcontroller chip I’m using was also becoming obsolete, and only available up until about a year from now. It is also implied that the entire family of microcontrollers was discontinued. I might switch to one of the ATMega microcontrollers used in Arduino products. That should at least ensure me reasonable support into the future.
So it looks like I’m in for a major circuit redesign, but it should ultimately simplify the circuit and require a lower-line microcontroller. All that will be needed is one or two digital outputs (or I²C lines) and one analog (A/D) input to read the caster cycle sensor, a far cry from the 32 signals in the current design. On the other hand, this will allow the PCB to shrink a bit, providing an easier fit (it looks like the current version will require removing the ribbon take-up spool). The new controller version would also move the cycle sensor and re-arrange some of the other parts.
And of course the firmware for the microcontroller will also change, but the basic logic should be the same. What would need to be adapted is timing code and USB handling.
All this while I’m still making the bracket to attach the power supply to the controller I have, to finally make it into a single unit with no dangling wires!
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