How to build self resetting load switch in embedded circuits

In many microcontroller projects we need to control loads such as relays, bulbs or motors. From microcontroller side we simply send signal that turns device on or off. Microcontroller normally don’t care whats going on further – is load switched on or is it failing. Of course we can build feedback and read voltage from sense resistor and then switch load off in case it draws too much of current. But sometimes relying on microcontroller to work reliable when it can hung due to overload conditions is not accepted. We need to use passive methods of protection. Few additional discrete components can make a big difference. Anthony suggests transistor based overload protection circuit which in normal conditions doesn’t doesn’t do anything. But once current exceed the limit, it shuts off switching MOSFET transistor immediately and thus probably saving the rest of circuit from frying. One simple solution is to use NPN transistor which base is connected to load current sense resistor. It value is selected so that voltage drop on load threshold current would open transistor and thus tie main… Continue reading

Constant current/power load with AVR controlled display

Constant current or constant power loads are handy testing tools especially if you work with power supplies or want to do some extensive battery testing. Kerry D Wong has designed pretty handy load electronics which is capable to sing constant current and constant power as well. In his design he used six IRFP150N MOSFET transistors to sink the current. Op Amps ensure that current is distributed evenly among all MOSFETs. Load parameters are controlled using Microchip MCP4921 DAC which comes with internal voltage reference. Arduino microcontroller can send commands to change voltage controlling load current. Arduino reads encoder to determine the DAC output. Kerry assembled his load on overkill heatsink. So he never had to worry about overheat. Continue reading

The Magnificent Helicontrol Project

Remote control toys are becoming some people’s favorite, as it bring unlimited of fun to the players. So, if steering miniature helicopters is your interest, then this Helicontrol is definitely your first choice! Well, Helicontrol is actually a small nifty USB gadget. It’s mostly being used to steer miniature helicopters or quadcopters, especially when the infrared remote control is requiring. The main purpose of the project is to develop a cheap yet easy to build IR remote control for helicopters. One of the features of the Helicontrol is it must easily attach to a PC without any modification. For this project, an USB is always the best choice, especially the Atmel (AtmelAvr) is known as the most useful microcontroller. However, it’s quite tricky to solder a TQFP34 package, but it should be fined after some practicing! Basically, the Helicontrol PCB are divided into four functional units, which as: AT90USB 1287 microcontroller: It included USB support, 128k flash up to 16 MHz AtmelAvr controller, crystal oscillator up to 16 MHz and capacitor. A MOSFET transistor (Up to six infrared LEDs to… Continue reading