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--- history [2020/05/20 11:37] – adminz
+++ history [2020/05/20 11:43] (current) – jtwine
@@ Line 6: / Line 6: @@
 Back in '09 I figured that since a voltage detection circuit was already possible, I wondered if there were any simplified implementations of them floating around.  Enter Microprocessor Supervisor circuits like the Maxim **MAX820** and **MAX792** circuits.  Those were a little heavyweight and could actually also implement the CMOS protection circuit that was already on the board, but did not want to have to do any mods to the board.  I wanted something that could just //drop in//.
-I never went any further with it because I was as confident in my abilities back then and did not even want to think about PCB fabrication.  Recently, when I got back into the Crowbar
+I never went any further with it because I was as confident in my abilities back then and did not even want to think about PCB fabrication.  Recently, when I got back thinking about [[https://jrtwine.com/Projects/Crowbar/|Crowbar Circuit]], I started thinking about other old ideas that might have a place in the Arcade and Pinball repair communities.  The LVR Circuit is the result of one of those trains of thought.
-Years ago, back when RGVAC was still fresh in people's memories I was reading about the woes caused by AR-IIs having their regulators go bad and doing really bad things like putting ~7 volts on the 5v line, killing most of what was connected to it.  I wondered if it was possible to have a voltage detector that would do something, like open a relay, if the voltage got too high.  Sounded simple enough but wondered why no one ever did it.
+I figure a target of $5 for just the PCB?  Dunno if I want to be selling assembled units.
-Looking further into it, I learned about crowbar circuits which are designed to short out a circuit (generally resulting in a blown fuse, tripped breaker, or power supply shutdown) and discovered that companies made voltage sensing chips that could be used to implement a crowbar circuit.  The Motorola (later On Semiconductor) MC3423 was of particular interest to me.
-Back in '09 while between jobs, I decided to try to implement something.  It ended up being a small tangle of wires and parts on perf board, but it worked and did what it was supposed to do - I turned up the voltage and it blew the fuse.  I started a new job soon thereafter and never thought about it again.
-However, I recently came across a post in one of the arcade repair related groups I frequent which was discussing "bulletproofing" an AR-II.  It turned out that not much had changed in the past 10 years or so - people would mention "bulletproofing," and then only talk about doing the Sense Mod with the occasional parts replacement.  I decided to dust off the old idea and take a stab at designing my first PCB.  As I was working with the schematic I realized that it could have applications beyond an AR-II, so I generalized it a little more and made it easy to connect to any power supply.
-The result is the **JRTwine Crowbar Circuit** device.  And while it does not technically bulletproof an AR-II, it can help prevent things from going too badly if the voltage regulator fails.  It also has other applications - anywhere you want to help protect a low voltage circuit from being damaged by overvoltage conditions.
-I am currently testing out different applications with different people right now.  The goal is to sell the device as either a bare PCB board, or as a partial kit containing the following components:
-  * MC3423 IC
-  * 8-Pin Socket
-  * 2N6505 SCR
-  * Fuse holder or fuse clips (depending on supply, maybe optional?)
-(Customers will have to provide their own resistors and LED.)
-I figure a target of around $10 works for the kit, and maybe $3-4 for just the PCB?  Dunno if I want to be selling assembled units.