Decrementing a four digit counter?

[Zucker]

I have built a four digit counter using an Allen Bradley photoswitch which
clocks four 74190s (Up/Down Decade Counters). When the beam from the
photoswitch is interrupted, the counter counts up.

I would like to be able to decrement the counter manually with a single
switch and have it act independently from the photoswitch (when
decrementing, the switch should be the clocking device, not the
photoswitch). This switch would have to drive the up/down pin AND the clock
pin of the 74190s at the same time. It doesn't seem like you would be able
to control both up/down and clocking operations at the same time due to the
propagation delays of the 190s.

Does anyone have any ideas on how I can decrement these 74190s with a single
switch?

Thanks,
Steve

 

[Geir Klemetsen]

I have built a four digit counter using an Allen Bradley photoswitch which
clocks four 74190s (Up/Down Decade Counters). When the beam from the
photoswitch is interrupted, the counter counts up.

I would like to be able to decrement the counter manually with a single
switch and have it act independently from the photoswitch (when
decrementing, the switch should be the clocking device, not the
photoswitch). This switch would have to drive the up/down pin AND the clock
pin of the 74190s at the same time. It doesn't seem like you would be able
to control both up/down and clocking operations at the same time due to the
propagation delays of the 190s.

Does anyone have any ideas on how I can decrement these 74190s with a single
switch?

Thanks,
Steve

I beleive you have to use a delay circuit. The button itself must be
conected to the up/down pin on the counter directly (no delay circuit
between).
The delay circuit must stay between the button and the clock-input of the
counter.

Geir

 

[John Fields]

I have built a four digit counter using an Allen Bradley photoswitch which
clocks four 74190s (Up/Down Decade Counters). When the beam from the
photoswitch is interrupted, the counter counts up.

I would like to be able to decrement the counter manually with a single
switch and have it act independently from the photoswitch (when
decrementing, the switch should be the clocking device, not the
photoswitch). This switch would have to drive the up/down pin AND the clock
pin of the 74190s at the same time. It doesn't seem like you would be able
to control both up/down and clocking operations at the same time due to the
propagation delays of the 190s.

Does anyone have any ideas on how I can decrement these 74190s with a single
switch?

---
You might be able to get away with something like this:

+V
|
[R]
| +-----+
|<--+----|D/U- |
| | | |
+---O [R] | |
| S1A | | |
| | | |
| |<--+----|>CLK |
| | | +-----+
IN--------O [C]
| S1B |
GND>--+-------+

if you used a DPST NC switch and you could assure that S1B opened
first and closed last, but I'm pretty sure bounce would kill you no
matter what.

Plus, you haven't mentioned anything about what the photoswitch
outputs look like and how you've got them connected to the counter
chain.

 

[Randy Day]

John Fields wrote:

[piggybacking]

Something like this? If I read the 74190 data
right, the clock line is positive-edge
triggered, and D/U=1 counts down. The switch
is SPST, normally closed.

VCC
+
|
.-.
| |R
| |
'-'
| .-----.
+------+--------------|D/U |
| | | |
| .-. | |
| | |R | |
| | | | |
| '-' | |
o| | __ | |
| +-------\ \ | |
--| | | |--|CLK |
| --- +-/__/ '-----'
o| --- C | OR
| | |
| | |
=== === in from photoswitch cct
GND GND

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de