[Coco] The Pepper board, a replacement circuit for the SALT chip.

[Rocky Hill]

 Please forgive the message formatting. I guess yahoo mail does not play nice andit injects fancy formatting into the message......


    On Monday, October 3, 2022 at 11:27:09 PM EDT, Rocky Hill via Coco <coco at maltedmedia.com> wrote:  
 
 Hi all,
About a year and half ago I made a circuit board that fully replaces the functionality of the SALT chip(Supply And Level Translator)that the CoCo 2's and CoCo 3's use. This board is a drop in replacement for the SALT chip and I call it the Pepper board.
I designed this board because I needed to bring one of my CoCo 2's back to life, always intendingto share the design so that others in my predicament could make one and/or improve on the design. Some people have already assembled a Pepper board and some have purchased a Pepper from me.
 The SALT chip is responsible for supply regulation, TTL<--> RS-232 (serial) level translation,cassette read operations, and driving the cassette relay. Without a SALT you can't do any of thatand with a partially working SALT you can do some of that.
the Pepper board offers some benefits other than the obvious one of having a working CoCo again.
1. The CoCo runs noticeably cooler.The Pepper board uses a switching regulator to provide the +5VDC to the CoCo and completely bypassesQ1, or the big transistor with the heat sink that gets really hot.
2. Uses less power.Because switching regulators are more efficient than linear or linear like regulators, it uses less power.
3. You don't need a transformer.You can directly power the CoCo via the transformer connector with a voltage range of about +9VDC to +40VDC.
You can probably already directly power the CoCo with +12VDC at the SALT chip input,
but the SALT chip depends on the roughly 13VAC that comes from the transformer to provide the -12VDCRS232 level for the bit banger. This means that although the CoCo will work, the serial port will not.


I just uploaded version 1.1.0.
This version has a different form factor so that it better fits all of the models of the CoCo's I have access to.I've tested it in the Following CoCo's
CoCo 2's
26-302626-302726-3134A26-3134B
CoCo 3
https://github.com/qbancoffee/coco_salt_replacement


In the next week or so I'll upload some pictures so that you can see what it looks like if youdon't want to load the KiCAD project and render it. 
Enjoy!





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