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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 18th Jan 2020, 12:42 pm   #1
jonnybear
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Default Simple Rotary encoder tester.

I wanted a quick check to find out whether a rotary encoder was working or not. so using a cut down PP9 case a SN74LS04, 7809 5 volt regulator caps leds etc, came up with this unit. could be used for other checks more inputs/outputs can be added if required.
John
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Old 18th Jan 2020, 2:37 pm   #2
bc312
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Default Re: Simple Rotary encoder tester.

John - great idea, but the 7809 regulator in the circuit diagram is missing the resistor to regulate the output voltage to 5 volts.
Mike
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Old 18th Jan 2020, 5:31 pm   #3
jonnybear
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Default Re: Simple Rotary encoder tester.

Quote:
Originally Posted by bc312 View Post
John - great idea, but the 7809 regulator in the circuit diagram is missing the resistor to regulate the output voltage to 5 volts.
Mike
Thanks Mike for pointing my mistake out,
Senior moment should be a 7805 not 7809 which is a 9 volt regulator.
John
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Old 21st Jan 2020, 11:57 am   #4
Herald1360
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Default Re: Simple Rotary encoder tester.

So the "resistor" will be 0R!
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Old 21st Jan 2020, 3:36 pm   #5
mhennessy
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Default Re: Simple Rotary encoder tester.

Alternatively, the 7404 could be replaced with the CMOS 40106. This should be pin-compatible, and will run from 3 to 18V, so no regulator needed. The battery life will be much-increased - the 7805 takes around 5mA quiescent and the 7040 will take around 3mA, whereas with the CMOS part, the only current will be that of the LEDs when on. Probably won't even need a power switch.

Downsides? Having to provide pull-up resistors (perhaps 10 to 100k). Might need to think about static protection - probably worth putting resistors in series with the inputs for that.

Nice use of for an old PP9
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Old 21st Jan 2020, 10:42 pm   #6
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Default Re: Simple Rotary encoder tester.

Be careful if you do that. Some rotary encoders contain TTL ICs and need a 5V (only) supply. And of course the output of such an encoder will be at 5V TTL levels.
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Old 21st Jan 2020, 11:53 pm   #7
mhennessy
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Default Re: Simple Rotary encoder tester.

The ones I've seen didn't contain TTL ICs - the electronics was integrated into the IR sensor (e.g. Spectrol 120EN) or Hall sensor (e.g. Alps EM11).

I would be amazed if any such encoder would be damaged by a PP3 via weak (10-100k) pullups. And I'm pretty sure that a TTL or CMOS (e.g. HC) logic IC would be just fine.

Of course, a constructive suggestion might have been the part number of a micropower 5V regulator to get around the ~5mA consumption of the 7805. How about the LP2950, for example? But frankly, I'd stick to my earlier suggestion - it was obvious to me at least that this was for mechanical contacting types only. If the OP had provided a 5V output terminal to power an "active" encoder, then that would have been different.
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