spamtrap1888 said:
Googling their street address shows they dissolved quite recently.
Also dissolved at the same address is Riscomp LTD. But Chiltern
Circuits still exists -- apparently all three firms shared directors.
There appears to be some current interest in using Autona amplifier
modules -- perhaps ask your question on a diy audio or guitar forum,
and someone would know where to find Autona schematics.
I'm thinking, too, that the circuit would have been documented in the
electronics magazines of that day. Or, that a similar circuit might
have been written up. I don't know if you have access to any circa
1990 electronics hobbyist magazines.
But, considering this is 20 year old technology, perhaps you'd like to
upgrade anyway?
Thanks both, good ideas which I'll follow up.
My motivation for sticking with this admittedly very old box is that it
avoids all re-installation hassle (changed connections, new rawlplug
positions, etc). And it goes against the grain to ditch it when all but
the re-entry works perfectly
Meanwhile today I'm going to dust off my shed workbench and breadboard an
add-on. That will hopefully regain the re-entry functionality, albeit at
the cost of adding an extra small case.
The idea is to use the N/C door sensor to trigger a 20 s monostable. That
in turn will enable an astable to give me a warning beep of around 2 Hz.
(Unfortunately, without the circuit diagram I can't confidently use the
existing 'sounder' for this.) When the mono ends it will trigger a short
pulse to a small relay (perhaps a reed type). A loop through the relay's
N/C contact to the original delay entry inputs of the CU will trigger the
alarm if it hasn't been disabled within the warning period (because these
inputs now act immediately, like the other loop inputs).
Apart from my general rustiness, I expect the main challenge will be to
ensure no problems arise with spurious triggering of the mono, such as
when power is applied, such as after a mains power cut. I plan to use CMOS
4001 and/or 4011, a few Rs and Cs and probably a transistor or two.
There's one other longshot approach I'm trying in parallel. By removing 4
screws I was able to get a good look at the circuit board. Its main active
component is a PIC16FC4. I know virtually nothing about PICs, but just in
case that *has* become faulty I thought it worth dropping in a
replacement. I couldn't find that specific one in stock anywhere so I've
taken a gamble and ordered a PIC16C54-XTI/P (8BIT CMOS MCU, 16C54, DIP18)
at £3.64.
Does all that sound reasonable?
