I can build from a schematic, but do not have enough knowledge to design
more than a simple circuit.

I need a circuit for an automotive application.
I have two relays that are switched on and off to achieve four states of
operation.
They are always powered with 12vdc and sequence by grounding them in the
following pattern:
A B
ON ON
OFF ON
OFF OFF
ON OFF

I am looking for a two button control where one button steps up through the
sequence and one steps down. The time between button press will be at least
2 seconds, but I guess I need something to make sure each press only
registers once (ie no contact bounce).
A plus would be a numerical (segment?) display numbering 1-4 for each
position.

Any help in setting this up or directing me to information on a circuit to
do this would be appeciated.

Thank you,
Gene

Gene,

You probably won't find a circuit for that, but why not take this as an
opportunity to learn how to use digital ICs. You can make it out of 4000
series CMOS, which will work directly from the 12V supply.

For the inputs, connect one side of each pushbutton to ground and the other
to a pull up resistor to the 12V. Add a capacitor to ground. That should
debounce the switch sufficiently.

For the outputs, the CMOS can't drive the relays directly so put your
digital logic outputs through a MOSFET such as a 2N7000 or whatever is
needed to handle the relay current. Add a catch diode for the inductive
spike off the relay coil.

You should play around to figure out how to do the logic between the inputs
and the outputs. If you get stuck, ask for help and we'll get you pointed
in the right direction.

John Musselman


"Gene Hudson" wrote in message
news:2mCde.43997$WI3.34729@attbi_s71...
I can build from a schematic, but do not have enough knowledge to design
more than a simple circuit.

I need a circuit for an automotive application.
I have two relays that are switched on and off to achieve four states of
operation.
They are always powered with 12vdc and sequence by grounding them in the
following pattern:
A B
ON ON
OFF ON
OFF OFF
ON OFF

I am looking for a two button control where one button steps up through
the sequence and one steps down. The time between button press will be at
least 2 seconds, but I guess I need something to make sure each press only
registers once (ie no contact bounce).
A plus would be a numerical (segment?) display numbering 1-4 for each
position.

Any help in setting this up or directing me to information on a circuit to
do this would be appeciated.

Thank you,
Gene

On Tue, 03 May 2005 03:37:34 GMT, "Gene Hudson"
wrote:

I can build from a schematic, but do not have enough knowledge to design
more than a simple circuit.

I need a circuit for an automotive application.
I have two relays that are switched on and off to achieve four states of
operation.
They are always powered with 12vdc and sequence by grounding them in the
following pattern:
A B
ON ON
OFF ON
OFF OFF
ON OFF

I am looking for a two button control where one button steps up through the
sequence and one steps down. The time between button press will be at least
2 seconds, but I guess I need something to make sure each press only
registers once (ie no contact bounce).
A plus would be a numerical (segment?) display numbering 1-4 for each
position.

Any help in setting this up or directing me to information on a circuit to
do this would be appeciated.

---
This would be a perfect application for a microcontroller, but I
suspect you don't have the tools necessary to do the programming, so
I've posted a CMOS logic solution for you on
alt.binaries.schematics.electronic.

Since there are only four states of on-ness or off-ness in which your
two relays can exist, I assumed that since the ON-ON state was the
first one you entered on your truth table, that was the one you wanted
to occur on power-up. If it's not, then post what you want the
power-up state to be and I'll modify the schematic for you. Also,
since there are only four states in which the pair of relays can
exist, the display comes up with '1' on power-up and can only count
to four.

--
John Fields
Professional Circuit Designer