[DML] Re: RPM Relay

["ksgrimsr" <knut.s.grimsrud@xxxxxxxxx>]

The RPM relay is a pretty simple circuit based on a 555 timer chip. 
The basic logic of the circuit is that a received pulse from the tach 
causes the 555 timer chip to activate for it's timeout period (a 
couple seconds). As long as it receives another tach pulse before its 
timeout elapses, the timeout resets and the circuit stays active. The 
net effect is that the relay activates on the first received tach 
pulse and then deactivates a couple seconds after the last received 
pulse.

For the cost of a new relay, it's really not worth messing with a 
malfunctioning one.

   Knut


--- In dmcnews@xxxxxxxxxxxxxxx, "Matt Spittle" <supermatty@xxxx> wrote:
> I think Knut Grimsrud published a schematic of the RPM relay in one 
of
> the previous newsletters he wrote.  You can probably do a search and
> find it.  
> 
> I had a bad RPM relay where it would run continuously as soon as I
> turned the key to the ON position.  That seems to sound like what
> you're indicating.
> 
> Matt
> #1604
> 







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