Simple Servo Tester

A little bigger than a postage stamp, the Simple Servo Tester lets you control two digital or analog servos without using a transmitter or receiver, just plug in your battery pack to start testing.

Use it to check your servos before installing them into your models or to center your servos when setting up linkages. The Simple Servo Tester can also be tuned to precisely center your servos - Some manufactures consider 1.520 milliseconds to be center while others use 1.500 milliseconds.

Use it anytime you want to operate a servo but don't want to get out your RC equipment!

This project was designed by W9GFO. You can get the kit from Gadget Gangster and download a PDF version of this howto.

Warm up your soldering iron and get started!

Step 1: Make: Parts List

Check to make sure you have the following parts:

Parts list

• Potentiometer Knob
• Green LED
• NPN Transistor
• Right angle pin header (9 pins)
• 555 Timer Chip
• 20k Right Angle Potentiometer
• Trim pot
• 2x Capacitors (0.1 uF)
• Rectifier
• Custom PCB
• 220k ohm resistor (Red-Red-Yellow)
• 3x 10k ohm resistor (Brown-Black-Orange)

Comments

[W9GFO]

(removed by author or community request)

[W9GFO]

(removed by author or community request)

[W9GFO]

(removed by author or community request)

[W9GFO]

Here is an updated schematic. The old one did not show that pins 2 and 6 were connected.

Thanks to Dustin for pointing out the omission.

[texasclodhopper]

(removed by author or community request)

[W9GFO]

 Because it's flipped around the wrong way in the drawing! Good catch, I'll fix it.

Rich H

[macman808]

what voltage is that battery?

[raykholo]

Most likely 4.8 volts.

[BOOJAN]

nooo...you are making a huge mistake. First resistors, jumpers and other small components, after that capacitators, diodes, IC's and finally potentiometers goes last. If you place the IC first you are risking to burn it while you are soldering other components.

[W9GFO]

Huge mistake?  I think that is a slight exaggeration.

I'll agree that it is good practice to save the chips until the end but for this board there are so few components that it really makes no difference. I also usually like to start with the lowest height components first, but again, this board is small enough that it is easier to just start in the middle and work outwards.

However, for anyone concerned about burning up the 555 chip, go ahead and put it in last, there is no reason why that wouldn't work just as well.

Rich H

[BOOJAN]

i exaggerate a little bit with that huge mistake, i was sleepy then and i've didnt know what i was writing, and i agree with what you are saying, first place the lowest height components, and then go bigger and bigger

[Unit042]

This is a nice project, but the schematic is quite confusing, perhaps you could add another schematic where the components are not all over the place? I mean, I don't intend to insult your efforts, it's just hard to read what with all of the 90 degree angle wire web....

Anyway, I just solder on an IC socket first, then transistors, because they have pins so close together. It's hard to solder around a tone of resistors, capacitors, etc, as my soldering iron tip is not quite what it sould be. (it hits other stuff because of its thickness, very annoying)

Just a thought.....

[bowmaster]

Or ypu could do what I do. Randomly grab something, solder it in, repeat.

[BOOJAN]

yup...my classmates are doing that...and they usually end up with burned ICs, a big smoke of capacitator, if it is a smaller value it will end up with huge BANG, burned transistors...etc...

[Sandisk1duo]

how about a servo tester for 4-5 wire servos?

[MACKattacksnipe]

Need video

[edfarina]

I modified the circuit to use batteries LiPo 2S or 3S, including a 4910 regulator taken fron an ESC burned.

[W9GFO]

The 555 chip used in the kit is rated for up to 16 volts. I have used it with a 2S LiPo but have not tested it with a 3s LiPo.  The thing to watch out for is the voltage going to your servos. Very few servos are designed to work on more than 6 volts.

In other words, the tester itself wouldn't need the regulator but the servos might. If you power the servo tester with a battery that is a higher voltage than your servos are rated for, you run the risk of damaging your servos.

Rich H

[edfarina]

 Exactly, Rich, use small servos that work with no more than 6 volts.
In 4910, I guarantee 5 volts to the servos.

[BlueFusion]

Would anybody be interested if I made a board available, either as gerbers, or to purchase (at cost price naturally)?

[paulm]

 Ok, wait a second here:

if they don't provide the "Custom PCB" information so we can etch one ourselves, this is just an advertizement

and its featured?

what the hell

[W9GFO]

You can use the schematic and lay out your own PCB if you want.

Rich H

[kelseymh]

While I understand that the PCB layout/silkscreen is GG's intellectual property, would you consider making the circuit schematic available? That would allow hardcore electronics types to do their own (presumably different) board layout, or breadboard it, or whatever.

[T2Pogi]

Kelseymh, check this out. this is the basic 555 design that will work the same way. Cut in a potentiometer between R2 and the capacitor C1 to make the timing variable.

http://www.ecelab.com/circuit-astable-555.htm

[computer_freak_8]

Thanks for this link! Another awesome schematic/explanation site added to my bookmarks. :)

[Gadget Gangster]

That's the basic circuit - there are a few little things added there (like the polarity LED), but nothing crazy.

[Gadget Gangster]

It's actually owned by W9GFO. I'm not sure if he has anything in a share-able format, but I'll ask him. It's a really cool circuit and a cool use off a 555 timer!

[danlab]

Does radio shack stock 555 chips? My normal electronics shop doesn't seem to have them.

[danlab]

Or should I just order them online?

[Gadget Gangster]

Really? I'm surprised that your electronics shop doesn't have 555's, they're really common. Try asking for a TLC555.

[danlab]

Ok i'll have to try that, is it an online only thing from radio shack?

[danlab]

So I checked the other radio shack (the one that is actually closer to my house) and they had several of them. Thanks for the input.

[danlab]

I asked one of the managers at the other electronics store and they hadsomeone come in and buy out their whole stock.

[crapflinger]

a little blurb about how it does what it does for us Luddites would be neat as well (surely couldn't be hard)

i have NO idea why i never thought of the painter's tape idea when soldering junk onto something like this (again...me=electronics N00B^{10)...that's such a simple idea}

[Gadget Gangster]

That tape is a super good idea. Servos are the little motors in R/C models and robotics projects (and a bunch of other things). You can use the Servo tester to make sure your servo is working correctly. By turning the knob, you can turn the servo.

[kelseymh]

I think "crapflinger" is asking for a beginners-level theory-of-operation. The pot changes the timing which drives the servo yada yada yada.

[crapflinger]

indeed, i know what servos etc are...i've done a lot of RC in my time...just wondering what the 555 is for and how the pots modify what it does etc..

[T2Pogi]

the 555 IC is wired as an oscillator. the pot determines the pulse width of the output (pin 3) any where from 1.5 ms to about 2.5mseconds (?) ; this pulse widh determines which way the servo motor will turn (left or right) and how much it will turn. the potentiometer works w the timing capacitor and the 555 functions as an astable multivibrator.

[Gadget Gangster]

Sorry! I wasn't sure. The 555 timer generates the pulses to drive the servos. Using the potentiometer, you're varying the pulse width and changing the position of the servo. Check out the wikipedia article on 555 timers, especially the part on astable mode.

The 555 timer is one of the most classic, ubiquitous integrated circuits - the wikipedia article is a pretty good read.

[crapflinger]

AHA! so basically you could (in theory) use this to drive any PWM driven device assuming that the board/electronics can withstand the supplied voltage?