W
Wes
- Jan 1, 1970
- 0
I would like to utilize the closure of an existing switch in my
pinball machine (Bally KISS) to trigge
r external circuitry. My initial
idea is to have a spinner switch create a pulse that would serve as a
clock for a decade counter (4017
).
So I researched the fundamentals of the switch matrix and how it is
scanned by U10 on a -35 MPU. The
manual shows the 2 wires (poller/send + switched return) on the MPU J2
connector to be at pins 4 and 14, respectively.
So initially, I figured that I could simply tap off these 2 wires and
feed them into an AND gate, usin
g the AND output for the clock pulse into the 4017 counter. BUT, here
is what I have found, and I'm h
oping someone can help me accomplish the goal. I'm thinking a
comparator or some sort of A/D converte
r is needed, but I'm inexperienced in the application/use of linear
ICs.
When I measure the voltage of the strobe/send wire (J2 pin 4), I do
get the expected pulse and I was a
ble to clock a 4017 directly with this send. Obviously, this doesn't
isolate the closure of the spinn
er switch, though.
The voltage at the RETURN (J2 pin 14) is where I start to lose it. I
expected it to be near 0V when t
he switch is open, and near +5V when the switch is closed. But what I
find is that this pin seems to
be strobing, and when I measure the voltage, I get around +3.2V when
the switch is open, and around +3
..4V when closed. I WAS able to see that this .2V delta is consistent
with other switches in the same
column of the matrix, so ....
I do seem to have almost what I need - I'm thinking I can determine
(theoretically) that the switch mu
st be closed if:
1) the send wire is "high"
2) the return wire is relatively "highER" (the .2V delta)
So, I THINK if I could just translate the +.2V delta into a logic
"high", then I could feed the AND ga
te as I originally thought I could do. Any insight into how I could
make this work would be greatly a
ppreciated.
I do realize that there are other (possibly better) ways to accomplish
this end goal - i.e. an isolate
d parallel switch, an opto-decoupler - BUT I'm intrigued by the idea
of tapping directly into the swit
ch matrix, and if I could get a handle on it, it would open up a world
of ideas for modifications with
easy installation (piggy back off the MPU J2 connector).
Thanks! -Wes
~
pinball machine (Bally KISS) to trigge
r external circuitry. My initial
idea is to have a spinner switch create a pulse that would serve as a
clock for a decade counter (4017
).
So I researched the fundamentals of the switch matrix and how it is
scanned by U10 on a -35 MPU. The
manual shows the 2 wires (poller/send + switched return) on the MPU J2
connector to be at pins 4 and 14, respectively.
So initially, I figured that I could simply tap off these 2 wires and
feed them into an AND gate, usin
g the AND output for the clock pulse into the 4017 counter. BUT, here
is what I have found, and I'm h
oping someone can help me accomplish the goal. I'm thinking a
comparator or some sort of A/D converte
r is needed, but I'm inexperienced in the application/use of linear
ICs.
When I measure the voltage of the strobe/send wire (J2 pin 4), I do
get the expected pulse and I was a
ble to clock a 4017 directly with this send. Obviously, this doesn't
isolate the closure of the spinn
er switch, though.
The voltage at the RETURN (J2 pin 14) is where I start to lose it. I
expected it to be near 0V when t
he switch is open, and near +5V when the switch is closed. But what I
find is that this pin seems to
be strobing, and when I measure the voltage, I get around +3.2V when
the switch is open, and around +3
..4V when closed. I WAS able to see that this .2V delta is consistent
with other switches in the same
column of the matrix, so ....
I do seem to have almost what I need - I'm thinking I can determine
(theoretically) that the switch mu
st be closed if:
1) the send wire is "high"
2) the return wire is relatively "highER" (the .2V delta)
So, I THINK if I could just translate the +.2V delta into a logic
"high", then I could feed the AND ga
te as I originally thought I could do. Any insight into how I could
make this work would be greatly a
ppreciated.
I do realize that there are other (possibly better) ways to accomplish
this end goal - i.e. an isolate
d parallel switch, an opto-decoupler - BUT I'm intrigued by the idea
of tapping directly into the swit
ch matrix, and if I could get a handle on it, it would open up a world
of ideas for modifications with
easy installation (piggy back off the MPU J2 connector).
Thanks! -Wes
~