YourITronics

Summer is here for those of us in the northern hemisphere and heat becomes a problem again. Fear not for here is a project for you to build your own room temperature controller.

This device uses two sensors to monitor temperature at two locations, inside and outside for example and depending on the measurements, it controls two external devices like cooling fans for example. Relays are used to turn on or off these external devices. You can chose to trigger the relays when the outside temperature becomes too high or when inside temperature becomes too low.

The microcontroller used is a PIC16F873 and controls all functions of the device. Port B drives the 7 segment LEDs, Port C is used for device designation, Port A controls the Relays.

The temperature sensors are LM35DZ. These sensors can measure from 0 degrees to 100 degrees Celsius and outputs 10mV per Celsius degree. However the 0V level is given at 2 degrees Celsius and since the project doesn’t use a symmetric (+/-)  power supply it’s lowest temperature that can be measured will be the 2 degrees Celsius. The sensor’s output after being amplified by LM358 Opamp is sent to PIC’s analog input.

The 7 segment LED display will show the inside temperature, the outside temperature and the preset temperature. The preset value is the threshold that will trigger the external devices. While this project is designed to maintain the room temperature around a certain value, the principle can be used in many projects like in one of those incubators where u can control a fan and a resistive heating element.

In the end i must say this is a very well documented project and everything is explained in great detail. The information is very well structured and besides complete schematic and code everything is very well explained step by step, including the actual building process. Happy soldering.

PIC-based Thermostat: [Link]

The idea behind this project was born when a friend asked me too take a look at he’s broken GPS unit (MyGuide 3000) to see if I can fix anything. I started checking various parts like voltage regulators, but found nothing wrong. The gps unit was still not powering up so I checked the cpu, an ARM9 from Samsung and found it broken. Of course I couldn’t do anything about that, because of the BGA package and the bootloader needed after replacing it so the gps unit became a source for parts. The most useful and interesting parts from the GPS were the LCD display and the GPS module.

The GPS module is a RoyalTek RGM-3550LP which has an integrated antenna and is powered by SiRF Star III technology. I immediately connected the gps module to my computer’s serial port(using a max232) to test if it was still working. To my surprise the gps module was working and sending NMEA compliant sentences. Then I had this idea of using the gps module as a navigation system together with a notebook computer, but notebooks don’t have a serial port so I had to use a UART to USB bridge.

The most common used UART-USB bridge is the FT232 manufactured by FTDI which is about $4 which is a fair price because you don’t need any external parts for this chip except some bypass capacitors and that saves you time and money. I never used the chip before but it was really easy to get it working. It even has this custom utility that let’s you program some features saved in the internal EEPROM like the maximum bus power and the product and manufacturer descriptor strings. Anyway these are the only two settings that I tinkered with, but the utility let’s you change some more stuff.

The next thing I had to worry was where to get the power for the GPS unit, because it needs 3.3V and the acquisition current is 50 mA. The FT232 has an internal voltage regulator which provides 3.3 V and 50 mA but I decided not to use that in order to extend it’s life so I ended up using the TPS2148 which is a 3.3V LDO from Texas Instruments. It’s specifically designed for USB peripheral power management, and it’s tiny package(MSOP-8) made it ideally for my application. The TPS2148 handles the current limitation so I didn’t had to worry about that either.

After figuring out the parts I was going to use and the schematic, I had to chose an enclosure for this project. The main target was to get it as small as possible but the limit was the gps module size, I couldn’t of got it smaller then the module . So I went and searched for a plastic enclosure, and I found one just perfect for what I needed, the PP85D from Supertronic. The gps module fits just nicely between the screw channels.

Then after I got the enclosure, I made the pcb using the photo etching technique.. I assembled and tested it, and to my surprise everything worked just fine from the first try. I’m usually not that lucky when I make stuff using new IC’s that I haven’t used before. Sometimes I don’t pay enough attention to the datasheet and I get some small stuff left behind and that messes my entire circuit. Anyway, happy as I was that everything worked from the first try, I put everything inside the enclosure and snapped some pictures of it. As a final note, this was a great project which I enjoyed making, and I really recommend you do something like this if you have a gps unit laying around.

more pictures:

parts list:

• RGM-3550LP gps module x1
• FT232RL x1
• TPS2148 x1
• capacitor 10uF x3
• capacitor 100nF x3
• led x1

schematics and board files were designed in Eagle and can be downloaded here.

This article has been supported by Wireless Matrix, which is a leading provider of Fleet GPS systems and wireless data communications services.

Keyless entry has been used for quite some time in automotive industry by most car manufacturers even though such a system may not be in their standard package. The owner receives a card or a small device, much like a remote control, and just by approaching the car, no buttons pushed, the car senses the master and opens its doors.

In this project is presented a method to build your own keyless entry system. Your RFID will be a Nike footpod which will send the secret code to its iPod receiver. This receiver communicates with an Arduino Pro Mini  through an iPod Serial Board. The Arduino listens for the right code from the RFID and gives lock/unlock commands.

You can give these commands to your car’s fob or adapt it to the internal wiring of the door’s lock/unlock mechanism. This can be pretty tricky for there are several systems used for door locking. In some European cars like Volkswagen, Seat, Skoda the command for lock/unlock is given on a single wire. For example if on this wire the computer sees a firm ground then it will unlock if it sees a resistance to ground then it will lock or the other way around. In these case you will need to use diodes or relays.

Asian cars usually have two wires, one for lock one for unlock. You will need negative or ground to control these wires. Things complicate however with the more expensive cars as they use vacuum systems or sophisticated computers inside the door. Usually these cars when equipped with a factory keyless entry system have a sensor behind the door handle that must be triggered in order for the doors to unlock, even if the car senses its owner nearby.

Powering our keyless system requires that you find a permanent 12V supply in your car. Look at fuse box, under the driver’s kick panel behind the steering wheel for thick wires and use a multimeter to measure the voltage. Do not trust thin wires as their 12V can disappear after car’s computer falls asleep. Usually that happens between 15 to 30 minutes after locking the car. Be careful with this because serious damage can be caused.

Other difficulty you can experience, as the project’s author did, is the car’s door locking settings. If you unlock the door but do not open it the car might lock it again after a short period of time. You can change these settings from the car’s computer with a diagnosis tool.

RFID Keyless Entry: [Link]

This is just a board I made to work with at school because normally I would not build anything on pic. I just wanted to show once again, that using the photo etching technique and some effective component placing you can obtain really nice results wether your building trough hole or SMT. The board has a quad op-amp for inputing and outputing analog signals and a max232 to provide a serial interface. It will be mainly used to gather data from sensors and send it on the serial interface to a computer.

I just came across this neat video on youtube, which shows some basic smt components sizes like resistors  &capacitors 0201, 0402, 0603, 0805, 1206 and TSSOP56 IC. The quality is great and I really recommend it to beginners.