[Humberto] from NerdKits is one of our favorite tipsters. We like how he can take a concept that seems so extremely complicated, in this case touch capacitance sensing, and present it in a clear and concise manner thats impossible to not love. As previously mentioned the most recent NerdKits hack is on touch capacitance; by using a resistor capacitor pair and some clever switch timing, anyone is able to detect the presence of a human limb. Now who’s going to be the first to adapt this concept further in their own hack?
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Easy touch capacitance
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Touch sensitive keypad
[Viacheslav] built a keypad that uses human capacitance to detect key presses. Unlike normal keys which close a physical connection, his project detects touch through the PCB substrate. He uses the ADC capabilities of an AVR ATmega8 to measure a change in capacitor charges for each sensor in the keypad.
He’s posted the schematic, Eagle files, and source code with his writeup. He also points to a document on the theory behind this: QMatrix Technology White Paper (PDF). We’re impressed at how simple the circuit is: a microcontroller, capacitors, resistors, and a homemade PCB.
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Capacitive discharge cutting
Capacitive discharge cutting provides more control than linear transformer versions. A very large capacitor is charged to a precise voltage and then discharged through the material to produce a controlled cut. The same device can also be used for spot and tab welding. A video of copper roof flashing being cut is embedded below. An example of a linear transformer can be found in our our How-to: build your own spot welder.
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Parts: SPI EEPROM (25AA/25LC)
Microchip’s 25AA/25LC EEPROMs are data storage chips with a simple 3-wire interface. The 25AA/LC is an SPI version of the common 24AA/LC I2C EEPROM. It comes in capacities of 128bytes to 128kilobytes. We looked at the smallest, the 128byte 25AA010A.
There are Bus Pirate demonstrations for most types of serial EEPROMs. Check out our previous 1-wire (DS2431) and I2C (24LC1025) EEPROM posts.
Continue below to see our test circuit and a demonstration of the 25AA010 EEPROM. We used the Bus Pirate to play with this chip from our PC. For a limited time you can get your own Bus…
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Parts: I2C real-time clock calendar (PCF8563)
The PCF8563 is a real-time clock/calendar/alarm chip with an I2C interface. This would be useful in projects where the primary microcontroller doesn’t have enough resources for an interrupt driven clock.
We demonstrate the PCF8563 using the Bus Pirate after the break. For a limited time you can get your own Bus Pirate, fully assembled and shipped worldwide, for only $30.
PCF8563 real-time clock calendar (Octopart search, $1.33). Datasheet (PDF).
The schematic above shows a bare-bones circuit for the PCF8563. It requires a simple external oscillator circuit with a 32.768khz watch crystal (Q1). The oscillator input pin needs an external…
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How-to: The Bus Pirate V2 with USB
The Bus Pirate is a universal serial interface tool, we use it to test new chips without writing any code. It currently supports most serial protocols, including 1-Wire, I2C, SPI, JTAG, asynchronous serial, MIDI, and more. We added some other features we frequently need, like pulse-width modulation, frequency measurement, voltage measurement, bus sniffers, pull-up resistors, and switchable 3.3volt and 5volt power supplies.
The new v2 family adds USB power and connectivity to the best Bus Pirate design yet. We also reduced the part count and cost wherever possible. If you want to get your hands on some Bus Pirate…
