Building the ServoBoss, a Servo Tester From





Introduction: Building the ServoBoss, a Servo Tester From

This is the ServoBoss. It is a servo tester capable of driving up to twelve servos simultaneously.
The kit is available from

It currently has eight programs.

Program 1 - Set milliseconds
Adjusts output to twelve servos (two groups of six) in .001 millisecond increments using pushbuttons. Displays pulse-widthsetting on LCD for both groups. The second group is reversed in all programs except for Dead Band.

Program 2 - Adj milliseconds
Using a pot, controls twelve servos while displaying pulse-width on LCD.

Program 3 - Dead Band
Alternately sends two pulses differing by X microseconds. X is adjustable from zero to 99 and is displayed on LCD. Increase the setting until servo jitters, then back down by 1 uS increments to find the Dead Band.

Program 4 - Cycle Servos
Enter High End, then Low End, then number of cycles, transit time and finally, the pause time. If number of cycles is 0 it will run indefinitely. Transit time is adjustable from 20 milliseconds up to 60 seconds. Pause time is adjustable from 0 to 60 seconds - anything under 10 milliseconds is ignored.

Program 5 - Sweep Servos
This program is nearly identical to Cycle Servos except that a button press is required for each stroke.

Program 6 - Set Three
In this program you set three pulse-widths. One each for Low, Center and High. Press one of the three buttons and it sends the servo(s) to the corresponding setting.

Program 7 - RX Input
Connect your RC receiver or other servo signal producing device and read up to six channels. Displays pulse width in 1 uS resolution. The incoming signal is passed on so that you can control your servos while reading the pulse widths.

Program 8 - Battery Pack Test
Displays voltage of battery pack, .01 v resolution, a few hundreths of a volt accuracy. This program always runs at start up. Good for checking for charged packs - just plug it in - no button presses required.

Step 1: Organize Your Work Space!

Clear a well lit space to assemble the kit and get your tools together.

Step 2: Inventory the Parts.

Make sure all the parts are there. If not, make sure to let the folks at GadgetGangster know right away.

Mouse over the second image to get a description of all the parts.

Step 3: Get Familiar With the Circuit.

Take some time to explore the circuit. Mouse over the images to get a description of the components.

To get a real close look, click the i in the upper left corner of the image and choose "original".

You will need to decide how you are going to power the board and servos.'

Option 1: Use the battery connector at the far right to power both the board and the servos. This is the preferred method.

Option 2 : Use a wall wart (up to 12 volts) plugged into the 2.1mm barrel jack to power the board. The 5 volt - 3 amp regulator then powers the servos. This would be OK for light duty but you can overload the regulator if you drive the servos too hard or drive too many servos.

Option 3: Use a wall wart (up to 12 volts) plugged into the 2.1mm barrel jack to power the board and a separate battery pack to power the servos. Very important - do not install the jumper that goes from the diode location to row T!'

Step 4: Now to Start Soldering.

If you took the time to familiarize yourself with the circuit you should be able to put it together with no further information.

Start by soldering all the jumpers and resistors on the front side of the board.

Generally, you want to start with the lowest (height wise) components first so that when you turn the board over to solder they don't fall out. Sometimes though you have to put things in that just won't stay. A simple solution is to use a piece of masking tape to hold things in place. The blue tape works best.

There is a small jumper going from 17, D to 17, E. Install it early on because there are two things above it.

Step 5: Calibrating

Calibrating is now an optional step. The ability is retained just in case it is needed but the default settings should work out pretty well. Until there is a need to enter the calibration menu I would recommend against it and I won't bother to show how it's done. Of course, if anyone needs it, just let me know.



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    25 Discussions

    How many servos do you think this think could handle if you used a wall wart to power it? I'd prefer not to use a battery pack and I need to power 5 high torque


    1 reply

    It would depend upon the wall wart that you use, the amount of current that it can supply vs the current that the servos need.

    The ServoBoss can control up to 12 servos simultaneously for testing however it was not designed to control servos that are under a load.

    To me, a "special instruction" is some information that does not appear available to resolve a problem by observation or reasoning.  An example:

    The LCD has 16 pins.  Installation of the socket header starts at C 1.  However, C 16 is occupied by the 103 cap to the pot.  Some resolution is required. 

    Another possible consideration might have been the mechanical interference posed by the crystal and the adjacent 104 decouplling cap as with the mounting of the 100K ADC, but are resolved by viewing the expanded "original" view.

    1 reply

     If you hover over the LCD header on the image above a text box will appear that explains that the last pin has been removed to make way for the cap.

    I've noticed that once in a while it is necessary to reload the page in order to get the mouse over feature to work. You should see a yellow outline around nearly every component, when you put the mouse on it, a text box will appear with an explanation. If you don't see the yellow outlines, try reloading the page.

    Where are the readable diagrams in step  3 & 4 of ServoBoss for wiring the back side of the circuit board as above and any other special instructions?

    2 replies

    The layout is located @  Special instructions have not been located.

     I'd like to help but I am not sure what you mean by "special instructions".

    Hi  Rich, Sorry that I haven't been around for a while. Work has been placing a load on me. Have you worked out all of the bugs yet? I'm really looking forward to getting my hands on this little toy. I'm toying on doing a "Show-And-Tell" at my local model airplane club. I would also like to know the price for both one piece and several ( your decision on how many ) so I could generate some interest at the club.  Any ideas when you might be convenient for you? 

    Also before I forget; How would I go about sending you payment data in a secret and secure format?  Thanks.

      Take care.


    Hi Rich. I thought that I would just check in and find out the status of your great project, the servo tester / exerciser. The last that I heard you were dissatisfied with some parts you have seen. Please let me know when you are ready to ship. BTW I have no problem paying you but I'm not cool with publishing my personal info in this area. 

    Take care and 73

    I am determined to have all of my boards made in my own country. I will not outsource. The Simple Servo Tester boards are made by Advanced Circuits in Colorado. The custom PCB for the Servo Boss will be made by them as well.
    I do not know where the Gadget Gangster Boss boards are made.

    Rich H

    Hi Rich. Long time no e-mail. I just read that you have made the Servo Boss available. Where can I contact you to arrange a purchase a kit from you? I want to use a credit card to purchase it from you and I feel more comfortable using a conventional website. If you have another suggestion I'm open to listen to what you have to offer.

    I await hearing back from you.


    Sorry to say that it is still not ready yet due to a problem sourcing the joysticks. The joysticks from the initial supplier were not up to spec. It'll probably be another month or so before they will be available. 

    Everything else is complete, it's just the joysticks that we are waiting on.

    Rich H

    Thank you for your quick reply :) The reason that I asked is the low price that is offerd for the kit. The pcb makers that I have looked at charge about $25 or more until you order 100pc or more. How can you offer a low parts count project at such an offordable price?

    Thanks, JZ

    I like your project. Problem is that I don't have the free time to part out the whole thing.  I could squeeze in the time to assemble if it came as a full up kit with the premade circuit board was included. Is there any chance that you could be persuaded to issue a full kit?  Please let me know. Thanks for your time.


    3 replies

    No persuasion necessary!  A custom PCB for this kit is currently being worked on. The PCB design is finished, it just needs to be tested.

    Rich H

    The best news I've heard all day. Thanks I needed that.  ;-)    Please let me know when it hits the street. BTW, I'm strictly a hardware guy. I tried to write code in computer class in 1985 and man did I stink at it. Machine language, (101101) Assembly (LDA SLF etc..) so please if you have a way to burn the code in as one option, PLEASE do it. I build pc's when ever I need to update my current workhorse but I just can't write code. Damn. You can't imagine what I would give to write good code. That has forced the postponment of several interesting projects. Ahhh well I digress. I gotta hit the sack. Good night and 73.

    The kit will come with the EEPROM already loaded with the code and there will be a place to install a programming header for those that want to write their own Spin code (or assembly).<br /> <br /> <a href=""></a> has a lot of really good <a href="">resources</a> for learning how to program microcontrollers. All the documentation, labs and programs are freely downloadable. On top of that there is an excellent <a href="">forum</a> where there are users of all skill levels that welcome anyone wanting to learn how to program. Do check it out if you are at all interested in learning to program.<br /> <br /> Rich H<br /> <br /> The new Servo Boss;<br /> <br />