Attiny25/45/85 PWM Generator and Servo Tester! Updated Code!




Introduction: Attiny25/45/85 PWM Generator and Servo Tester! Updated Code!

Hello, in this project I want to show you how to build a PWM generator with a Attiny processor. It is very easy to build and a nice project for starters as also for professionals. You will need some electronic knowledge and some knowledge about Arduino. It wont be to hard, because i already wrote a code for the Attiny, which you can use.

This PWM generator also works as servotester, it supports all kinds of servos, which dont need more then 5V


Operating voltage: 5V
Max PWM current: 1 A
PWM frequency (by now) : 500HZ , I am trying to make that changeable, if you know how, let me know :)
High effency
small size
small prize ;)


So lets get started!

Step 1: Material and Tools

The materials will cost less then 4$, also you need a Attiny programmer, i used an Arduino Uno!


2 Resistors (450 OHM)
1 Resistor (1 kOHM)
1 BC548 NPN Transistor (or equal)
1 BC516 PNP Transistor (or equal)
some Jumpers
1 Potentiometer (10 kOHM or higher)
serval kinds of terminals (picture 1)
some unisolated wire
1 eight pin IC holder
1 Attiny (25/45/85) I used the Attiny45
some PCB


soldering iron
a cutter knife
a pincer
a attiny programmer (Arduino Uno)
a breadbaord

Step 2: PCB Layout

Here is the PCB layout i made, beacuse of the less parts it is super simple and easy to build!

The PWM output will be on pin 2 of the Attiny and the analog input will be on pin 4. The BC558 is used as Inverter and as a first amplifier.
After that the BC516 is used to get the current to a maximum rating of 1A, what is actual very good and can drive a pc fan or a dc Motor!!!!

note: the PWM signal is only against 0V not against 5V!

!!! take care dont wire the Transistors wrong, it can cause a shortcircuit!!!

Step 3: PCB Layout #2

Now there is a special about this PWM generator. It has the ability to drive servos, the problem is that different manufacturer sue different pin connections for their servos. That makes problems, when you want to test serval kinds of servos, so i Made a connector system which allows you to change the output pins of the PWM generator!

In picture 1 you can see the system, it has 3 jumper pads, one for the PWM signal, one for 5V (+) and one for 0V (-).
As we change the Jumpers ( picture 2 ) we can change the ouput of the Servo connector on the right side.

!!! NEVER have some Jumpers in a row, it will cause a short circuit and can destroy your PWM generator!!!

In picture 2 the jumpers are correctly plugged!

Step 4: Assemble It!

My PCB looks now like this, I added a few sticker, terminals and a small potentiometer, to make it look nice.

Its your choice how it will look like :)

Step 5: The Software!

now its time to program the Attiny25/45/85! for this i use a Arduino Uno with a AttinyShield, but you dont need a shield! You can also do that on a Breadboard.

A smal how to:

1: Add the Attiny core to your Arduino software ( )
2: Wire your Attiny and Arduino like in the Picture 1
3: open your Arduino program
4: go to File>Examples>ArduinoISP
5: Upload it
6: open a new window
7: go to Tools>Board>Attiny45(internal 8 MHZ), click on it
8: now open your code ( code for the project in the next step)
9: Upload it.......wait.....wait.....
10: Error : avrdude: please define PAGEL and BS2 signals in the.....
       is okay

11: now your Attiny is programmed! (yay)

Not working?

Check out a full Instructable about it by @randofo its awesome and helped me alot

Step 6: The Code

Now its time to program the Attiny!

I wrote a code for this project, its made for the Attiny. By now it only supports 500HZ PWM, but i will update it as soon as i can.

My goal is 50HZ, beacuse 50 HZ are needed for a servo.

You can get my code from Git Hub:

Just upload it, as described in step 5, plug your arduino in the PCB and it should work.

The is also a code aviable for the Arduino, dont change them, otherwise it wont work.

Okay, here is a fixed code for servo testing only, it isnt a PWM signal, but it controlls servos!

And also here is a 15 HZ version of the PWM signal!

Step 7: Testing

Finally, your own personal PWM generator using a Attiny25/45/85 is ready for testing! :)

First plug your 5V power source in, it is recommended to use one with a current monitor, because if the current go straight up to more then a few Ampere, you made a mistake (troubleshooting in the next step).

Mine uses a current of 10-20mA

I used an old oscilloscope, but you can also build your own one!

Just check out my other Instructable, How to build a Oscilloscope!!

Important: never place jumpers in the same row!!

Video of the Output signal!!

Step 8: Troubleshooting

Current goes to high:

shortcircuit on the PCB

Built around transistors fals

Built around IC fals


No PWM at the output:

make sure you measure against 0V not against 5V

check connections on the board ( maybe something not soldered)

IC not correctly plugged in

Oscilloscope right set?

PCB catches fire

... -.-

Step 9: Ideas!


Instead of a potentiometer you can add a heat-dependent resistance and instead of a servo you can add a computer fan to control the speed of you pc fan.

Its just an idea, to add sensors instead of a potentiometer...

Step 10: Finishing


You made your own PWM generator, yes that is your own merit!!!

Also thank you for reading, check out my other projects, and feel free to vote for me in a contest! :)


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    8 years ago on Introduction


    I wrote my own pwm controller for a different microcontroller without using any built in pwm module using the following method:-

    1. set up an interrupt to generate 50*255 times per second. - so that you can time every 1/50th of a second in 255 little time slices.

    2. use a counter variable to count the interrupts as they happen and reset every 50 interrupts.

    3. use another counter variable then to count from 1 to 255 interrrupts in that 1/50th of a second.

    4. when the first counter resets to zero then set the pwm output to high. then, when the second counter hits your target width (by comparing its count with the pot input (suitably scaled to fit 1-255 range) you set the pwm output low.

    so, every 1/50th of a second the output goes high and then after a period determined by your pot value it will go low until the end of that 1/50 of a second when it will go high again etc etc.

    hope that helps.


    jakers dad


    Reply 8 years ago on Introduction

    Okay, interresting, i will try it :)

    Thank you!!


    Reply 8 years ago on Introduction


    sorry, I mangled that explanation a bit. You actually only need one interrupt counter if you dont need to keep track of the number of seconds. see attached image which hopefully will make things clear.

    of course you may need to take into account that position control only wants pulses between 1 and 2 mS long and not the full 20mS of the 50Hz period. My pwm was for speed control rather than position (and i was controlling acceleration so i needed the seconds info) but all the same it will work and is amazingly easy actually.

    good luck

    Jakers dad

    jan hendrick servo controller small.jpg

    5 years ago

    code works great for my application at internal 1mhz driving a mosfet for a 12 volt motor


    6 years ago on Introduction

    Is it possible to use the BC517 instead of BC516 transistor?
    many Thanks


    7 years ago on Introduction


    In order to test servo, why do you need transistor on the signal output?


    Reply 7 years ago on Introduction

    The idea is to also directly drive Motors and lamps with PWM :) you can remove it, when you only want to test servos!


    7 years ago on Introduction

    sorry, what could be replacement for BC516? here i can not get it.


    8 years ago on Introduction

    About the PWM frequency - if what you say is right, your "Arduino" is using the highest prescaler for the Timer1 (that one used to generate PWM on that pin). So to increase frequency, you just have to decrease prescaler. You might try macro from core_timers.h from tiny_core:
    Timer1_ClockSelect( timer1_cs_t cs )
    as timer1_cs_t cs you might try some of the values:
    #define TIMER1_PRESCALER_VALUE_1 (1)

    #define TIMER1_PRESCALER_VALUE_2 (2)

    #define TIMER1_PRESCALER_VALUE_3 (4)

    #define TIMER1_PRESCALER_VALUE_4 (8)

    #define TIMER1_PRESCALER_VALUE_5 (16)

    #define TIMER1_PRESCALER_VALUE_6 (32)

    #define TIMER1_PRESCALER_VALUE_7 (64)

    #define TIMER1_PRESCALER_VALUE_8 (128)

    #define TIMER1_PRESCALER_VALUE_9 (256)

    #define TIMER1_PRESCALER_VALUE_10 (512)

    #define TIMER1_PRESCALER_VALUE_11 (1024)

    #define TIMER1_PRESCALER_VALUE_12 (2048)

    #define TIMER1_PRESCALER_VALUE_13 (4096)

    #define TIMER1_PRESCALER_VALUE_14 (8192)

    #define TIMER1_PRESCALER_VALUE_15 (16384)

    Of course without #define's and values (I'm just lazy enough to copy-paste from .h file ;) )
    If not, you might try to change the TCCR1 register value according to the attiny85 datasheet, page 89 and 90.
    Hope this will help you.
    P. S.
    now probably tiny85 is using prescaler #15, so using #14 should increase frequency twice ;) to about 1kHz


    Reply 8 years ago on Introduction

    Thank you, I will try it in the afternoon...

    I already tried the TCCR1 register value, it didnt work good, but i will keep trying!



    Reply 8 years ago on Introduction

    Oh... I see, that you want to lower the frequency, not to increase... So that may be hard, because you'd need to increase prescaler, but it's impossible because of using the biggest now. But you're using Arduino Core, so why won't you just use Servo library?


    Reply 8 years ago on Introduction

    Thats a good questions, by now I dont thought about it :D:D


    8 years ago on Introduction

    measuring 5 times and delaying 10ms each time limits the PWM frequency -- measure ADC once like every half second or every second - and keep the pwm static for the rest of time. - this way you get rid of the unneeded delays, and can increase frequency.

    and BC516 is only 500mA. (or I´m missing something?)

    otherwise - nice little gadget.. :)


    8 years ago on Introduction

    nice work. looks good. you can make a servo tester with a 555 timer


    Reply 8 years ago on Introduction

    Thank you, but with a NE555 it wouldnt work good, because the NE55 cant make a good PWM, it can just change the frequency, what can be used with some extra parts ( capacicators & co ) to fake a pwm, try it with a oscilloscope... :P