Preset a counter IC

[krjhitch]

I'm trying to figure out how to preset an up/down counter in a way that's tied into the circuit that doesn't involve pushing buttons.

In the circuit below I've tried to create a switch that I can turn 'on' and then my counter starts at 6 and counts down, displaying the number on a 7-segment LED.

Is what I did with the transistor correct? Does it work? Does it not work? Do I need to 'pulse' low somehow instead of just holding it low and then holding it high? I'm trying to grasp exactly how you can preset a timer. Eventually I plan to put a dip switch in to make the number configurable, as well as chain some ICs to make it multi-digit, but for the time being I'm just trying to figure out how to load the number.

 

[ericgibbs]

I'm trying to figure out how to preset an up/down counter in a way that's tied into the circuit that doesn't involve pushing buttons.

In the circuit below I've tried to create a switch that I can turn 'on' and then my counter starts at 6 and counts down, displaying the number on a 7-segment LED.

Is what I did with the transistor correct? Does it work? Does it not work? Do I need to 'pulse' low somehow instead of just holding it low and then holding it high? I'm trying to grasp exactly how you can preset a timer. Eventually I plan to put a dip switch in to make the number configurable, as well as chain some ICs to make it multi-digit, but for the time being I'm just trying to figure out how to load the number.

hi,
There are lots of problems with that circuit.
74LS and 74xx series are powered by 5V not 9V.
You cannot connect the transistor without resistors.
Check the output 'sense' of the 7447 , its for common anode LED's.

The way to get a auto reload is to use gates to sense the count, then cause a load.
EDIT:
You must not connect the /BO and /CO to 0V.!

The unused CLK input must be high for the active clock to count.

 

[krjhitch]

I was aware of the CA vs CC issue for the LED, I just hadn't gotten around to rewriting it.

I recall reading the +5V for the ICs, I can rectify that, and I originally had /BO and /CO tied to another IC in the schematic, I just removed it to simplify my question.

Can you explain what I should be looking for as far as the resistor with the transistor (What am I trying to accomplish?) And what do you mean by auto reload? And by using gates to sense a count and then cause a load you mean I should set up some logic gates to see if the switch is thrown?

How would I set that up so that the /LOAD is low while presetting, and high while counting?

 

[ericgibbs]

I was aware of the CA vs CC issue for the LED, I just hadn't gotten around to rewriting it.

I recall reading the +5V for the ICs, I can rectify that, and I originally had /BO and /CO tied to another IC in the schematic, I just removed it to simplify my question.

Can you explain what I should be looking for as far as the resistor with the transistor (What am I trying to accomplish?) And what do you mean by auto reload? And by using gates to sense a count and then cause a load you mean I should set up some logic gates to see if the switch is thrown?

How would I set that up so that the /LOAD is low while presetting, and high while counting?

hi,
If you give an example of a count that you require to create a parallel reload, I can suggest a way on how to do that.

For example is the reload count is '6' you would use a NAND gate on the LS193 outputs Q1 and Q2, its output would go to /PL.

OK.?


EDIT:
Just noticed you want to count down to ZERO from '6' , so use the /BO to cause a /PL to reload the '6'

 

[krjhitch]

OH! I see what you're saying. If I wanted 6,5,4,3,2,1,0,6,5,4,3,2,1,0.

Right now it would do 6,5,4,3,2,1,0,9,8,7,6,5,4,3,2,1, right?

 

[ericgibbs]

OH! I see what you're saying. If I wanted 6,5,4,3,2,1,0,6,5,4,3,2,1,0.

Right now it would do 6,5,4,3,2,1,0,9,8,7,6,5,4,3,2,1, right?

hi,
Look at this LTspice image of a recent circuit, it will give you an idea of the gating required.