Everything you need to know about diodes


Diodes are commonly used discrete semiconductor device. It has many uses and purposes. Its operation is based on PN semiconductor junction characteristics. Depending on diode physical and chemical properties it can behave very differently. Together with other electronics components diode can be used for voltage clipping, multiplying, rectifying, signal, demodulation, protection and even more. Elektro-labs have written pretty nice review of diode types and their common uses. Simplest and probably most recognizable is regular diode which is used in switching, protection rectification circuits. Another common diode type is Zener which is used for voltage stabilization, then list goes on LEDs and photo-diodes and finishes with more exotic ones – tunneling diodes and varactors.

Handy voltage transition indicator circuit


On battery operated circuits you simply need a simple way to test the voltage. In other hand complicated circuits don’t look very attractive. So for keeping things simple and low cost, Einar Abell suggests his single transistor voltage indicator circuit. It is able to detect transition between two voltage levels on battery. Simply speaking, if circuit is powered from 9V battery, then it will transition from green to red indicator when voltage foes from 7.1V to 5.8V. One downside of this indicator is that it drains about 1mA of current. For any battery this is nearly not acceptable. To avoid constant drainage simply drop a push button to test voltage when you need.

Efficient way of driving latching relays

If you need to keep relay turned on or off for a long time, then standard relays may not be best solution. First of all in order to keep relay switched, power must be applied. If you are using mechanical relay, then coil must be constantly energized. This way relay draws power and for battery operated equipment this is not acceptable. SSR relays might be a better solution, but signal still need to be applied in order to keep it turned on. In such cases there are latching relays used. These relays keep their state after switched and power is removed. They are common where relay need to be on or off for long time. Controlling such relays is a bit trickier than regular ones. First of all relay can … Continue reading

Few tips for building reliable SPI interface


Many SPI tutorials use common notation of bus design where each device is directly in parallel connected to SCK, MISO, MOSI and CS lines. This normally works without problem, but in general, there can be problems when more than one SPI device is on the bus. DorkbotPDX rises several issues that can occur on poor design. Here are three suggestions for better SPI improvements: Use pullup resistors on all chip select signals. Verify tri-state behavior on MISO: use a tri-state buffer chip if necessary. Protect bus access with SPI.beginTransaction(settings) and SPI.endTransaction(). Pull up resistor helps to prevent response from multiple devices at once. This might come from poor software design when CS pins aren’t initialized properly. Second problem is with MISO pin. In fact some SPI devices doesn’t enter tri-state … Continue reading

Self sustaining solar powered charging platform


When deploying remote electronic device there is always a dilemma how to power it. You normally want to provide long therm power source and if it can recharge during operation, then things are even better. If you are thinking on building embedded project outside, then you should consider using renewable power sources like sun and wind. SwitchDoc Labs has been working on handy platform that helps achieve a bit of power independence. Their main focus is to provide solar tracking for small solar panel which can charge batteries, power embedded boards like Raspberry Pi or Arduino, and report parameters to apps. So called “SunAir” have everything you need to deploy independent system which takes care of tracking sun with two photo-resistors, servo motor and limit switches. Solar charge controller ensures … Continue reading