Wednesday, June 10, 2020

Analogue Board


Well the Digital board is working fairly well... well enough for me to bother starting on the Analogue board anyway. Problems with the Digital board are the usual Z80 issues with stable clocks and making sure that we have a long reset pulse. The new CMOS Z80 doesn't seem very interested in running but the old NMOS one is OK. There is a resistor missing from the UART/opto isolator circuit but with the addition of the resistor it all seems OK and the NMI works and the CPU collects the data. I have Ruby script to feed in the SYSEX settings but really need the Battery backup in place first. The Analogue board has had a couple of small tweeks like a switch mode regulator instead of the rather brutal original linear one and a negative 5V generator so a simple DC wall wart will suffice through a standard barrel connector. I was thinking that the filter design could be redone for a Shruthi filter board... maybe one day...

Wednesday, May 27, 2020

Getting There... slowly...



The Panel PCB has returned from JCL and under the circumstances was pretty quick! Some hard to find parts came from eBay and some new, but a bit tarnished, parts have come from Digikey. The digital board seems to run OK and has HCT TTL parts to try and lower the power consumption a bit. Need to program up the EPROM so I can do some more testing...

Saturday, April 18, 2020

50ck3t5 all the way...

Well the PCB is back and I have decided to socket everything so I can experiment with newer logic families and CMOS versions of the VLSI. The front panel PCB is dragging a bit...

Friday, August 23, 2019

Knobs & Panels...

Trying to maintain the original look as much as possible... Without the strange lumps of rubber...

Thursday, August 15, 2019

EPROMs

To get my Z80 board into a functioning state I need to get the code into it... One interesting thing that I had sort of forgotten in the modern world of Electrically Erasable memory is the venerable EPROM. I have memories of cycling through dozens of 2716 EPROM's to debug some Z8 assembler late into the evening for a contract I was doing... My old EPROM programmer needs an ISA bus processor and it hasn't really been used for 20+ years. Even the newer one at work, which uses a parallel port, is non starter for pretty much any hardware from the last 10 or so years. The quickest way out is this thing from e-bay, that seems to work OK... It is still cheaper that the old old EPROM programmer from 1987ish and there has been 30 years inflation since then.

Tuesday, August 13, 2019

Z80 all over again...

Back to the Z80! It's been a long time but that was the processor of the 80's...

Thursday, August 8, 2019

Making a monosynth...

Well for a laugh I am making a early 80's monosynth! This is the donor keyboard from a rather dodgy Japanese Hammond Organ -- the Piper II. The rest of the build is getting there. The Control electronics is done 100% and the front panel PCB (quite large) is at about 98% -- just need to do the filters and output stages on their own PCB.... Hopefully for completion in the very short term!