Wednesday, March 20, 2019

Simple Digital Clock with PIC16F628A and DS1307 and 7-Segment LED display

In this new project I am again using PIC16F628A microcontroller. The goal is simple digital clock with 7-segment LED display and the clock will have no additional functionality - no alarm, no seconds digits, no date. The latter can be added in the software though. For the RTC chip I chose DS1307. For the LED display I used Kingbright CC56-21SRWA.

Friday, March 8, 2019

3-wire fan adapter with fake 'tach' signal

This is a quick small project that I design this evening. My wife complained about loud fan in her computer, so I purchased the quieter fan I can find in Sofia - SUNON HA80251V4-000U-999.
It's only 22 dB noise but unfortunately it is two-wire fan without yellow tach signal wire. The computer will work fine but at every startup it will beep some fan error and will require confirmation to continue.
I spend some time researching the subject and found that the tach signal is square wave signal and usually have two pulses for every rotation. So the frequency of the signal will be: F = (RPM / 60) x 2.
For example a 2000 RPM fan will have 67 Hz tach signal. 
One unusual thing about 3-wire fans is that the tach wire is connected as open collector.

The solution is very simple - small adapter board with square wave oscillator followed by a NPN transistor with open collector. The frequency of the oscillator is not that important - from 33 Hz imitating 1000 RPM fan to 200 Hz for 6000 RPM fan. I chose the classic two transistor astable multivibrator:

I soldered the components on a small piece of perfboard. The fan doesn't come with a connector but only with two strip wires, which I soldered directly to the board. On the other side I soldered standard 3-wire cable with molex connector. The adapter worked as expected - the computer recognized the fan and started without problems. I checked with HWiNFO, and the program reported around 2600 RPM for this fan.

This adapter can also be used entirely without a fan - the computer will still think there is a fan connected. Of course if your CPU burn out it will be only your fault :)

Friday, February 8, 2019

Push button ON/OFF + Soft start v.3

This is a revamping of an old project: "Two versions of soft sart". There were reports in the comments that the circuit doesn't always work. I have tried myself on a breadboard and indeed - the schematic works with chips from Nexperia and doesn't work with chips from other manufacturers. The problem is in the input stage of the schematic - the push button.  There is a capacitor in parallel to smooth the bouncing of the contacts but the pulse gets too long and is registered by 4027 clock input as more than 1 impulse. Without the capacitor schematic will work if the push button is high quality, otherwise, again the 4027 will detect more than 1 input signals. To combat this problem I tried different methods an here I present two of them.

Saturday, April 8, 2017

Download links problem

Hi there,

From some time now the links for downloading project files in my blog are not working. This is because most of them are from dropbox and they for some reason changed their sharing policy and now all public links has been disabled and I must edit all the links one by one. Things get further complicated because I use URL shortening service (, and long story short  - it will take some time to fix all the links.

UPDATE: September 08, 2017
Most of the links are now fixed.

UPDATE: 29.01.2019
Fixed some more dead links and for some of the projects I also added Gerber files.
If there are still dead links, let me know.


Wednesday, September 23, 2015

100MHz frequency counter with LCD display

Update November 26, 2015:
I made a full project with preamp/signal conditioning and power supply with soft on/of switch. It is published here.

This is the same as the previous frequency counter but the output is on the 16x2 LCD display.
For more details about how it work look here:

Wednesday, August 5, 2015

100MHz frequency counter

Couple of weeks ago I purchased from eBay one of these amazingly cheap an useful modules with MAX7219 LED driver and 8 digit LED display. It is ideal for frequency counter project. The problem was the absence of library for PIC microcontrolers. Luckily, I found a great library for Arduino and I reworked it to be compatible with PIC. The schematic of the frequency counter is actually almost the same as the previous . It uses PIC16F628A microcontroller with external 32.768kHz watch crystal attached to Timer1 to generate 1 second time base. Measured signal is fed to pin3 (RA4) which is counted by Timer0.