Counter / Trigger project

[ViperTech]

I need some ideas for a project I'm working on. I'm using a hall effect to count revolutions of a pulley. I'd like to dial in a preset pulse count from the hall at which the circuit would send a positive or a negative pulse to reset.
For example, at every 4 input pulses (or whatever count I'd choose) the circuit sends a pulse out.
I thought of a 4510 or a 4516 but am not sure this is the easiest design.

 

[vne147]

What is the maximum number you would like the circuit to be able to count up to?

 

[crutschow]

Either one should work for you. For BCD you could use a thumb-wheel BCD encoded switch to input the preset value to the counter jam inputs of the 4510. Then the counter will count down from there to zero at which time the /Carry Out signal goes low. This /Carry Out signal can be run through an inverter to enable the Present Enable line and load the thumb-wheel setting at the end of the count for the next count cycle. You can cascade as many counters as desired for any count length with one BCD switch for each counter.

 

[ViperTech]

vne147 I need it to count between 1 and 24 pulses. Crutschow, I'll try a frequency divider using a 555 and test to see if it's precise enough. If not, I'll go ahead with a BCD. Thanks for the ideas.

 

[crutschow]

vne147 I need it to count between 1 and 24 pulses. Crutschow, I'll try a frequency divider using a 555 and test to see if it's precise enough. If not, I'll go ahead with a BCD. Thanks for the ideas.

For 24 pulses you would need two counters and two BCD switches (which would allow counts up to 99).

So how are you going to dial in the preset number of counts with a 555?

 

[ViperTech]

Well, it's definitely not as precise but I'll be using the 555 as a frequency divider. Configured as a monostable multivibrator, when the 555 is triggered by a pulse at pin 2, the RC network will first have to be completed before any subsequent pulses at pin 2 can trigger the circuit again. I'll use a pot in place of the R allowing me to dial in my pulse width. I'm testing it on my prototype and although it doesn't have the precision of a nuclear sub, it's pretty good so far. I'll compare the signals from the hall to the output of the 555 on an o'scope tomorrow to see if the in/out ratio is consistent.