one output to many inputs best practices

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sabireley

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I am sending a PWM signal generated by a 555 timer to 8 AND gates (2-74LS08). The other input of each AND gate is tied to the output of a 4017 counter so the PWM signal is switched to 8 diffent motors as the counter advances. The circuit works and seems to be reliable.

My questions are:
From a best practices perspective is it ok connect ths single output to 8 gates? Is there a better way?
Are there any issues I should look out for when doing a PCB layout? Noise perhaps?

Thanks!

Steve
 
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The 74LS08 has very high impedance inputs, which means they need very little current to "turn on".
I don't see why it would be "bad practice".
 
Another way is to use a true binary (74xx161) counter and a 74XX138 decoder/demultiplexer. If you have to short-cycle the counter then you'll need to decode the top count, but if you're using all 8 outputs of the decoder, it might save you an IC.
 
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Thanks Roff!

I just looked at the data sheets for both and it looks like it could work. It would save a chip and the short counting is not necessarily a requirement since the user will reset the device manually after n number of servos have been actuated. I will see if I have a LS161 laying around. I know I have some LS138's.

One thing I did not mention is the pulse to increment the 4017 counter is from an external device that outputs a 250ms 6v pulse. Every time the user pushes a button on the external device, its output goes high for 250ms. I share the ground between the external device and my circuit.

Thanks!
 
74XX163 or 74xx93 should also work. There are also up/down counters (74xx193) that would work.
 
The PWM is really a servo signal that adjusts based on the voltage applied to pin 7 of the 555 counter and is separate from the signal used to clock the counter.
The counter increments each time a pulse pulse comes in from an external device. The pulse is user controlled with a button on a remote control transmitter.

I need to study the datasheets a bit more to figure out how to wire the devices to achieve the same end result as using the 4017 and AND gates.

Thanks!
 
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