Re: [stella] Analog electronics help.

Subject: Re: [stella] Analog electronics help.
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Mon, 27 Jan 2003 12:24:49 -0500 (EST)
I don't know why this isn't working.  What's the coil current of your relay?
Maybe the transistor isn't sinking enough current?  Try making the resistor
1k instead of 10k.  Also double check your relay wiring...there are ways
to build an oscillator with just a battery and a relay.  Yes you can use a
MOSFET.  Maybe a 2n7000 or something similar.  BTW, what do you mean by 5v
applied to the mosfet from both sides?

If it were me, I'd just use a PNP transistor as a switch.  Try a 2n3906.
Connect the emitter to 5V, and put a 1k resistor from the base to your
XC95144 pin.  The collector will be the VCC output.  Note that this is
an inverter, so the control pin should be low to turn on VCC....

Oh wait.  Is the XC95144 a 5v part or a 3v part?  If it's a 3v part, this
won't work.  The output has to go all the way to 5v to turn off the PNP.
And it could cause the oscillations in your relay driver if the pullup
is weaker than expected by the designer of your circuit.  So try a smaller
resistor (1k) if you use that circuit, etc...

Hope this helps!

On Mon, 27 Jan 2003 mickey_m@xxxxxxxxx wrote:

> Anyone willing to help with an analog question?  I am ok with digital, just
> not analog.
> I have a cart I made that allows me to download games to it so I can play on
> the 2600.  I am trying to add a cart reading function to it (you plug a cart
> into my cart and you can dump it to pc).  Which means I need to apply power to
> the line that normally is the VCS power (I do not use VCS for power).  My
> logic is all handled in a CPLD XC95144 and I would like the power to be
> applied when it says.  Pins on it can only supply 24mA.  I tried using a relay
> with a switching transistor (something like this:
>, but I cant get it to work right,
> the relay oscillates on and off.  I tried manipulating the bias resistor and
> tweaking it other ways, but no go.  So I am guessing that I need to to it
> another way.
> Can I use a MOSFET?  If I do, is there going to be an issue when my cart is in
> the VCS, there will be 5V applied to both sides of the MOSFET from separate
> power sources.  Is this a problem?
> Thanks
> Vern
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