Category: AVR

Digital Thermometer BreadBoard testing

Thermometer V1.0 was built at my very first steps on microcontrollers and generally in electronics about 2008. Then i was still writing embedded software in assembly as a starter. It was a big challenge for me to drive the HD44780 LCD Display and the ADC of the Atmega8 using assembly. I remember, i was writing and testing about a month to make it work. Searching for bugs on both hardware and software. By the way when you develop both sides hardware and software, debugging is the most difficult thing. Υou don't know where to start from, searching for bugs, software or hardware? I also had came across with the problem of making a division and that wasn't that easy. I had to write a whole function to do it (in C you can just write the symbol / and division is done). In assembly if the division is by 2 you can easily shift the value right but if it isn't what you can do?

This project wasn't something admirable but it was much a lesson for me. I learnt a lot of things from this like writing assembly, learning how the LCD  works and how to drive it with the correct timing! Every difficulty you come across is a lesson for you!. Of course when i saw it working (on breadboard) i felt so happy like a kid.

I also remember a classmate of mine sawing him the code and talking about how many hours it took to me to make this thing work and him telling to me "Oh that's what you made? this is very easy… I made the same thing in about half an hour". When i asked him how he did it, he revealed me that he had just copied some C code (about 20 lines) of a book he found when mine was about 600lines and i knew where is each word in the code. Well the answer is yours… You can make things the easy way but you have to know that someone else had worked for you to make these things easy for you and he is the one who has learned the more! If you want to learn don't choose every time the easy way.

Well here i post some photos of the circuit. It was my first homemade double side pcb using short wires for vias and soldering components in both sides which finally didn't work :P. For a reason i don't know i have lost the Eagle Schematic and Board Layout. I have only the code and the photos. So i post what i have.

As i remember i have used ATmega8, LM35 and HD44780 LCD Display. Also LM7805 has been used for power supply.

 

Digital Thermometer Digital Thermometer

Digital Thermometer Digital Thermometer

The Assembly code can be downloaded at the following link

DOWNLOAD HERE

Two years ago i modified a scanner replacing its mechanism and all the internal electronics with UV lamps converting it to an UV exposure box for PCB prototyping. By the need of making my life easier and not waiting for the pcb to be exposured i designed an AVR timer to automatic switch off the lamps after 1 minute of exposure which was much enough for the PCBs. Here is the circuit

The circuit

This was one of my first completed projects from design to production. As you can see the scheme isn't that good and there have been by passed some capacitors at the power supply. But the circuit works with no problem.

B1 is an AC voltage rectifier which in compination with the C1 (filtering AC) converts the AC to DC voltage. The LM7805 comes to regulate the voltage at 5Volt for ATMEGA8 power suppling. The AVR drives two 7-segments D1 and D2 for timer digits displaying, a buzzer SG1 to beep when lamps are switched off and a relay K1 driven by a NPN transistor Q1 to switch on and off the UV lamps. Also there is a diode D3 connected in parallel with the relay's inductor to prevent reverse voltages burning the transistor. Switch S1 is used for AVR restart and switch S2 is used for timer reset.

Testing on breadboard

Timer-bread board testing

The finally PCB printed with the UV exposure box

Timer-PCB

The timer

The timer

 

 

The code is written in C and the delay is produced by a delay routine and not by a timer. This because when i had designed the timer i didn't have enough experience with timers so it was much easier and familiar for me to use a delay routine. The device is accurate enough for uses like the one i designed it for. The code is small, very simple and understandable.

DOWNLOAD HERE

The IV-12/11 vfd tubes need 1.2Volt for the filament about 100mA each. In my clock project i'm going to use 6 tubes so the total draw current will be about 600mA which is to much for a linear regulator like LM317. The LM317 can be used, but it will be need a big heat sink to keep it cool. So i designed a step-down converter based on MC34063A, a pulsed regulator, which is also power efficient.

I could have been used a resistor in series with the filament but if any tube filament get burned then the other 5 will draw more current and get burned too. Also i could have been used the AVR to regulate this voltage than using the MC34063A but there wasn't more free space on the chip.

MC34063A Step Down Converter design.

The design is based on the MC34063A's datasheet. In this design i regulate the voltage to 2.5Volt because the tubes want to have a negative voltage about -1volt to get fully powered off. So i have put two diodes in series (with ones kathode connecting to others anode) connecting the negative filament pin to GND. By this, each diode works as a supply voltage providing 0.6V x 2 = 1.2Volt.   2.4V-1.2V =  1.2Volt which is the supply voltage needed for powering the filament.

 

Protoboard testing

MC34063A ProtoBoard