[sdiy] 8080-based synth reliability

[Richie Burnett]

Maybe it failed due to ESD/transient pickup on the doorbell wiring 
eventually causing damage to the micro, since you said that it would 
occasionally go off for "no reason."  Switching transients in house wiring 
and nearby lightning strikes can couple some ferocious voltage spikes into 
runs of un-shielded wire.  But then 40 years is pretty good going!

-Richie,

-----Original Message----- 
From: Dave Brown
Sent: Friday, October 06, 2017 8:54 PM
To: 'Synth DIY'
Subject: [sdiy] 8080-based synth reliability



This is definitely DIY related and somewhat synth related in that it is a 
digital 3 voice synthesizer.  In late 1976 I designed a dedicated 8080 based 
three voice PWM synthesizer as a doorbell.  The code was based on a program 
called Music for the Processor Technology Sol-20 computer.  I had to 
disassemble the program to get it to run on a basic 8080 system using a 
single 2708 EPROM and two 2114 static rams.  It used a simple transistor 
driver for the speaker.  The 8080 is unmarked so I think it might even be an 
engineering sample.



This system has continuously run for approximately 14,870 days or nearly 
356,880 hours.  Well this week it died.  The processor is just absolutely 
lifeless.  I had another 8080 from the same vintage but at least marked and 
replacing it brought the system back to life.  Note that in the 40 years the 
2708 has not forgotten even though the guaranteed retention is only 10 
years.  I think it will outlive me.



It was a really progressive program for the time.  This doorbell also 
includes a RS-232 interface so I could compile new music to upload to it for 
special occasions.


Dave



David J. Brown

Modular Synthesis, LLC

http://modularsynthesis.com






Virus-free. www.avg.com





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