Pulse Counting

John Burrow

All,

I'm planning to build a pulse counter from Steve Vorres design. This design uses 74LS590 Pulse Counter, a 74HC165 Parallel to Serial and, in my case, a Stamp

I started out breadboarding the Pulse Counter, 'cause my knowledge of electronics is almost non-existant. I'm grounding out the pulse counting pins (11 and 13), and observing·the chips output·via LEDs on the 8 output pins (15 and 1 to 7). I get·an almost·predicable, but very strange sequence of LED's lighting. (I was expecting to see the usual 'binary addition' sequence). I get more like 2 set of 4 pins, with each set counting independently.

So should I be using a pull-up resistor on the input (pins 11 and 13)? For the LED, I'm assuming my don't need resistors as they havn't burnt out yet. Or could I be overloading the chip with the LED's?

If anyone has an example of a circuit that I can copy, that would be helpful.

Thanks, John









·

kwinn

John, first thing is you do need current limiting resistors on most leds. The only exception are those leds with built in current limiting. In your case 180 ohms to 330 ohms should work.

You also need levels or pulses on several pins.
Pin 14 - /OE needs to be low to enable the output on pins 1-7 and 15
Pin 13 - RCLK needs a pulse from low to high to transfer the count to the output register
Pin 12 - /CCKEN needs to be low to enable counting
Pin 11 - CCLK is the input for the pulses you want to count
Pin 10 - /CCLR clears the counter when it is low. It needs to be high while counting

Some of these can be pulled high or low permanently for some applications, but active signals for RCLK, and possibly /CCLR are needed.

Download the data sheet for the info.