Build a 9-digit Pulse Counter for under $20

Recently I was fixing a piece of equipment and wanted a pulse counter to verify a stepper motor system. The existing linear slide was failing, but had a non-standard TPI. The step output was already programmed into a PLC. I had a programmable motor drive, but needed to know how many steps were commanded for a given linear move so I could electronically gear the system to a new linear slide.

PulseCounter 002

That’s when I found the MC14453 3-digit BCD counter from ON semiconductor. ON semi has integrated three decade counters with an oscillator that multiplexes the 3 digits of an LED display. You pair it with an MC14543 7-segment decoder to have a three segment counter. You can cascade as many of these two chips as necessary by using the overflow output to clock the next stage, and feeding the first scan clock to the next multiplexer. I made a 9-digit counter, but you can do any multiple of three.

I used a MAX232 to drive the input of the counter. It’s a bit of a waste of the MAX232′s abilities, but the MAX232 does a great job of handling a wide range of input signals and it’s only about a buck.  The chip can handle inputs from +30V to -30V, and still triggers between .5 and 1.5V with a 5V digital output. It also offers +/-15kV ESD protection on the inputs. With this capability you can sample a variety of different signals without any level shifting (even AC). With a few more input components (current limit resistor, zener clamp, series capacitor) you could capacitively couple the signal and measure anything. I wanted good low frequency performance so I skipped that part.

The parts cost about $6 per 3-digit stage. They are all available at Digi-Key. Part numbers:
MC14453: MC14553BCPGOS-ND
MC14543: MC14543BCPGOS-ND
MAX232: 296-6940-5-ND
7-Seg display: 160-1544-5-ND

The only problem with this arrangement is that the MC14543 is driving the LED segments, so it’s limited to less than 10mA drive current. That makes the segments a bit dimmer than I’d like for easy viewing. If I was doing it again I’d get some cheap transistors to run more current. The display is capable of 20mA.

The schematic can be found in the datasheet for the MC14553. Keep reading for the layout and schematic for my build.

Click images for full-size.  I mixed up the bias for the hold and reset inputs, if you use momentary off-on switches replace reset with R25 and hold with R26. Otherwise make sure the switches are normally closed.

PulseCounterLayout

PulseCounterSchematic

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Thursday, April 29th, 2010 Electronics

20 Comments to Build a 9-digit Pulse Counter for under $20

  • [...] to reverse engineer a stepper motor on a linear actuator that he was repairing, so he built this 9-digit pulse counter to keep track of how the motor was being controlled. It's a pretty standard circuit, however his [...]

  • [...] roughly $20 to build, this 9 digit pulse counter is an excellent example of home built tools. The builder, [Josh] found himself repairing a device [...]

  • [...] to reverse engineer a stepper motor on a linear actuator that he was repairing, so he built this 9-digit pulse counter to keep track of how the motor was being controlled. It’s a pretty standard circuit, however [...]

  • BiOzZ says:

    so what is this “strobe” lead in the schmatic and where do i wire “hold” ?

  • imsolidstate says:

    The “strobe” signal is the input latch enable, or LE on the schematic. It’s normally low. When taken high, the latches hold the last value of the counters. This value is sent to the display multiplexer. Note that the counters can continue to count, but the display will retain the number of counts at the time LE went high. When LE returns low, the latches will display the actual value of the counter, which may have increased while the display was holding, if it was receiving clock inputs.
    If you want to prevent pulses from actually reaching the counter instead of just pausing the display, use the “disable” line. Pulling this line high will ignore pulses sent to the clock input.
    You can wire “hold” to either one as desired.

  • [...] roughly $20 to build, this 9 digit pulse counter is an excellent example of home built tools. The builder, [Josh] found himself repairing a device [...]

  • [...] at $20 to build? This 9 digit pulse counter is an excellent example of home built tools. Josh, The builder found himself repairing a device and [...]

  • [...] a 9-digit Pulse Counter  – [Link] Tags: Counter, displays, MC14453 Filed in Test/Measurements | 1 views No Comments [...]

  • [...] Build a 9-digit Pulse Counter  – [Link] [...]

  • Ron Smith says:

    Hello
    Where do I get a PCB for this counter? Thanks

  • John Jakubowski says:

    Do you have a PCB available for this circuit?

  • imsolidstate says:

    I just updated the post to include my schematic and PCB layout. I don’t have any finished PCBs, pretty much everything I make is one-off. Maybe when I’m done with school I’ll have time to make batches.

  • John Jakubowski says:

    Thank you! What Layout/Schematic software do you use? I’ve never found one with components like the LED displays.

  • imsolidstate says:

    I use EagleCAD. Eagle has LED 7-segment components, but I had to make the three digit part in my library. With Eagle you just set up your own library and then make any components that aren’t in Eagle’s library.

  • Barry S says:

    I have two goals. 1.Build this as a learning experience. 2
    Use the counter to count pulses generated by a Mercedes diagnostic trouble code provision on pre 1996 model vehicles. I have electrical skills but no experience with building this sort of thing. Any tips would be greatly appreciated. Thanks

  • imsolidstate says:

    Start with the datasheet for the two chips. The schematic is there. Then decide if you are going to breadboard it, or maybe use perfboard if you can’t etch your own boards. Wire it up just like in the schematic. The MAX232 also has a schematic in the datashseet. The output of that chip is the input to the counter. The MAX232 buffers the signal and protects the counters from voltage spikes. You can wire the Merc’s diagnostic wire to the input of the MAX232 and it will trigger as long as the signal crosses approximately 2.5V. Good luck.

  • Barry S says:

    Thanks for your help! This will be fun

  • [...] to reverse engineer a stepper motor on a linear actuator that he was repairing, so he built this 9-digit pulse counter to keep track of how the motor was being controlled. It’s a pretty standard circuit, however [...]

  • missa says:

    what are the values of components needed here????

  • KOS says:

    Can it be “converted” into a 1hz resolution frequency counter?
    any hints?

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