8M to create 50-800 12v pulse/second

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dadx4

New Member
experienced programmer new to microcontrollers and very new to electronics.

Love my picaxe so far.

I would like to use my 8M to create 12 volt pulses at a variable frequency. (50 - 800/sec) I'm imagining varying the PWM connected to a relay? Adjustment from analog input thru a potentiometer?

If anyone could help (especially with specific components) I would greatly appreciate it.

-DADx4
 
Technical

Technical

Technical Support
Staff member
Don't - you cannot connect a PWM output to a relay, you will quickly destroy it. They are not designed to be rapidly switched on and off.

You can however use the PICAXE pwm and or pwmout commands to generate a pwm stream to drive a discrete component (transistors, FETs etc.), which can then switch your 12V load.
 
B

BeanieBots

Moderator
As mentioned by Technical, your relay will be destroyed very rapidly at that sort of switching rate, if in fact it even switches at all. (some can takes several 10's of mS to switch).

The "optimum" way to interface a load to a PICAXE depends largely on what the load is.
What sort of load are you interested in switching? LEDs, lamps & motors all have different requirements.
If it is a motor, do you need to drive it in both directions?
 
D

dadx4

New Member
the pulse generator would emulate the 12v pulses generated by an auto ignition and read by the tachometer. I would like to play with this using my picaxe18x. I guess the answer would be whatever load associated w/ stepping these pulses down to 5v then into a picaxe 18x read by the "count" function.

Thanks for the quick responses and all the help.
 
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MartinM57

Moderator
Why bother with the 12v bit? In the real implementation you'll just use a potential divider (and probably zener protection) to get the 12v signals from the real system down to 5v for the picaxe to proecess

I am prototyping, right now, a picaxe based tacho and ignition advance display device.

I've got one picaxe producing the waveforms that will come from the igniton system (5 lines of code!) and one picaxe receiving them, decoding them and displaying the results on two four-digit LED displays (about 75 lines of code!)
 
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MartinM57

Moderator
In that case I don't really understand what you mean by:
<<the pulse generator would emulate the 12v pulses generated by an auto ignition and read by the tachometer. I would like to play with this using my picaxe18x. I guess the answer would be whatever load associated w/ stepping these pulses down to 5v then into a picaxe 18x read by the "count" function.>>

What are you playing with? Testing the tachometer by itself using a picaxe to provide 12v pulses? Using a picaxe to verify the tachometer - if it's off the shelf, why do you need to do that? Or something else?

I'm confused ;-)
 
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