555 servo tester
Prototype of 555 based servo controller

555 Servo prototype

Big projects continue to be scary, so I make and document smaller ones. First old project to live - 555 servo tester.

After modding servos for continuous rotation i wanted to test them, being too lazy for software I searched the web. First schematic that I found was Gadget Gangster's 555 servo tester. It works by generating pulses in inverted mode (since 555 "cannot" make duty less than 50%) and then inverting them with one transistor not gate. Next schematic from the web used a diode to make smaller pulses but used frightening control-voltage pin.

555 based servo tester schematic

555 Servo Schematic

So, I made a design that uses minimum number of parts. I also used 10k potentiometer, because pot is the most expensive part in design and 10k seemed like the most common value. Although the design is simple enough to change it for whatever components you have lying around. I drew the schematic in KiCAD, not because i had to but because drawing only the schematic is actually more convenient than in Eagle.

[It was pointed out that the schematic is not working. I looked at it and fixed it. The resistors were swapped. I'm sorry]

8 thoughts on “555 servo tester

  1. hello but please can upload the PCB. And it is strong or is just for testing, I look online and not found.

    me no speack inglich

  2. Random one from parts bin. If you can't decide what to buy, buy the cheapest small signal one.

  3. Thanks Jaanus! I'll give it a try on a breadboard this weekend.
    Comparing your schematic to similar ones I see no VCC on pin 8 or GND on pin1. Is this on purpose?

  4. No, kicad symbol for 555 didn't have power pins visible. In reality everything must be powered.

  5. Hello,
    I was wondering if the system would work the same with a tactile switch instead of the pot. ?
    Have you tried this ?

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