Category: Handy Circuits

Turn-key PCB assembly services in prototype quantities or low-volume to mid-volume production runs

Reusing LiPo power supply for your embedded project

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Reusing LiPo power supply

Every electronics device needs a power supply. In many cases we just go with AA batteries, 9V + regulator, wall mounted adapter and LiPo cells. First ones are obvious enough – easy to obtain and pretty safe. Lithium technology batteries falls in to different category. These cells carry much more capacity than casual batteries, but also are more dangerous and sensitive to too much discharge and overcharge. This is why in almost all cases LiPo batteries come with small PCB attached to them. This circuit at least takes care of disconnecting battery in case of discharge bellow threshold (2.7V). In battery packs this situation is more complex. Proper circuit should monitor individual cells and disconnect whole pack if at least one cell reaches the threshold. But in reality cheap battery packs lack individual protection. So in case of failure of single cell, whole pack is condemned. Karman suggests not to throw such battery packs away for electronics disposal, but instead take them apart and check if there are any of individual cells alive. They can be reused in other projects.… Continue reading

Using DIP switch to select voltage you need

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In many cases you simply need a voltage source that could be used right away. It may be 5V, 3V or other like. Many battery operated electronics require voltages that are multiply of 1.5V – single cell. So for instance if device requires 4 AA batteries then it total voltage is 6V. Jason is a fan huge of garage sales where he can find lots of ideas and materials for his projects. But he wants to make sure if devices works properly before purchase. Due to variety of battery types he didn’t want to carry a bag of batteries around. So he came up with nice idea p DIP switch controlled power supply. As you can see there is nothing actually new or extraordinary. An LM317 power regulator is used to adjust voltage to right level. DIP switch seems to be convenient way of selecting the voltage. Each switch is connected through resistor that allows adding 1.5V per step. Supply is powered from 9V battery. So this makes useful battery replacement. Output wires have alligator clips to connect to device… Continue reading

Connecting LED matrix in to modules

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LED matrix is a great way to display things. Normally single matrix bloc is quite small. In order to get bigger picture you need to combine multiple modules. The best way is to use shift registers. Will built a modular LED matrix design that makes it easy to combine several 8×8 LED matrix blocks in to bigger one. He used MAX7219 driver chips. They can be interfaced using SPI interfaces. And multiple chips can be daisy-chained. This setup requires few lines to control. Each module has convenient connector which allows quick plug-in many of them in a row. Continue reading

Temperature sensor and storage for embedded projects

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Temperature sensor and storage for embedded projects

I2C interface allows connecting multiple devices using two wires. This interface is very popular in sensors, memory chips and IO expanders. R-B designed compact breakout board where he placed MCP9802 temperature sensor and 24LC512 EEPROM. Module is convenient to use as temperature sensor with ability to log values in to near by memory. So if you decide to unplug sensor – history of data goes with you. 512Kbit EEPROM gives enough space for storing data. Digital temperature sensor is capable of measuring temperatures from -55ºC to 125ºC. Prototyping board is designed so it could be easily plugged in to prototyping breadboard. Continue reading

Nice little switch for your next microcontroller project

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power toggle switch

When building a microcontroller based project we don’t think much about power switch. Usually this is a simple switch that connects power on and off. More sophisticated designs may require smarter solutions like toggle switch. J.R. Stoner has been playing around with interesting circuit called Powach. This is a standalone toggle power switch with built-in debounce and power LED indicator. Circuit is built using Schmit triggers and P-channel MOSFET. Switch can pass up to 2A of current which is enough in most embedded projects. The switch turns power on practically immediately, while turning off requires longer hols. It prevents from accidental turn off. Great feature. Board is designed to fit in to breadboard, while circuit itself can be a nice piece for your next MCU project. Continue reading