> The relay is an omron g5v-1, 150mA. I tried using just about every value for
> the bias resistance. I found three levels of resistor values. If the
> resistance is too high, it wont switch. If the resistance is what seems to be
> the right value, it oscillates. If the resistance is too low the output of
> the xc95144 shuts off, possible a protecting circuit? I feared I could have
> damaged the part so I tried news pins and new parts, same reaction. My wiring
> has been check one million times.
That's a pretty heavy coil current. There are cheap relays available that
require less. But that's separate issue. The 3 resistance ranges are exactly
what I would expect. Try replacing the NPN with a darlington configuration
(see attachment). That way you can turn the relay on harder with less current
from the '144 chip.
>
> > 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?
>
> My cart has its own power source, a wall wart (500mA) and a 5V regulator.
> When I go to dump a cart, I want my cart to power the dumped cart through the
> card edge. This has to be a switched connection, because when my cart is
> placed in the VCS, both my cart and the VCS would be applying 5V. So If I
> used a MOSFET, it would have 5V from 2 sources, one on each end. Is this ok?
OK....I think I understand. Under no circumstances should you connect the
5v line in the cart port to an external 5v regulator. The only common power
connection should be ground. But without a schematic, I don't know what you
want to do exactly, so I can't really give any suggestions for the right way
to do it.
> I dont want to damage my VCS.
Good to ask first! :)
> > 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....
>
> I thought of using a PNP but didnt try because the XC95144 is setup to output
> 5V, but it really only outputs max 3.7V, which wouldnt switch the transistor.
Ok, I was afraid of that. But you can still make that work. Can you configure
the '144 output as an open collector? (i.e. pulldown only). Or tristate. Or
however you want to say it? If so, you can use a pullup resistor from VCC
to the base of the PNP to turn it off, and use the '144 (with the 1k resistor)
just to turn the PNP on. I think the pin can be tristated, so this should
work. If you can't do this, then use a diode at the output of the '144 to
make it pulldown only.
But again....it would help if you could post a schematic of your power scheme
so I could know what to tell you.
-Chris
> I think the problem lies in the XC95144. I have a 20Mhz clock running the
> logic and I think I am getting some funky feedback or RF interference.
>
> I dont really want to try the MOSFET idea until I know I wont harm anything.
>
> Thanks for the help guys,
>
> Vern
> >
> > 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!
> > -Chris
> >
> >
> > 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:
> > > http://www.rentron.com/images/rely-drv.gif), 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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