Resistance in Motion: What You Should Know About Variable Resistors

Adjusting the volume dial on a sound system, sensing your finger position on a touch screen, and knowing when someone’s in the car are just a few examples of where you encounter variable resistors in everyday life. The ability to change resistance means the ability to interact, and that’s why variable resistance devices are found in so many things.

The principles are the same, but there are so many ways to split a volt. Let’s take a look at what goes into rotary pots, rheostats, membrane potentiometers, resistive touchscreens, force sensitive resistors, as well as flex and stretch sensors.

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Hackaday Prize Entry: MyComm Handheld Satellite Messenger

We live in a connected world, but that world ends not far beyond the outermost cell phone tower. [John Grant] wants to be connected everywhere, even in regions where no mobile network is available, so he is building a solar powered, handheld satellite messenger: The MyComm – his entry for the Hackaday Prize.

The MyComm is a handheld touch-screen device, much like a smartphone, that connects to the Iridium satellite network to send and receive text messages. At the heart of his build, [John] uses a RockBLOCK Mk2 Iridium SatComm Module hooked up to a Teensy 3.1. The firmware is built upon a FreeRTOS port for proper task management. Project contributor [Jack] crafted an intuitive GUI that includes an on-screen keyboard to write, send and receive messages. A micro SD card stores all messages and contact list entries. Eventually, the system will be equipped with a solar cell, charging regulator and LiPo battery for worldwide, unconditional connectivity.

2016 will be an interesting year for the Iridium network since the first satellites for the improved (and backward-compatible) “Iridium NEXT” network are expected to launch soon. At times the 66 Iridium satellites currently covering the entire globe were considered a $5B heap of space junk due to deficiencies in reliability and security. Yet, it’s still there, with maker-friendly modems being available at $250 and pay-per-use rates of about 7 ct/kB (free downstream for SDR-Hackers). Enjoy the video of [Jack] explaining the MyComm user interface:

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Very Large Touchpads for Very Old Computers

Way back when most of our demographic was in diapers, engineering workstations had huge touchscreens for plotting drawings in CAD programs, drawing, and just about everything a Wacom tablet does today. Finding one of these touch pads now is a fool’s errand, more so than finding the computer it was attached to, but [Daniel] figured out a way to relive those days of large touchpads and old computers with a resistive touchscreen and an MSX computer (portuguese, google translatrix).

[Daniel] is using a touchscreen normally used for a monitor, and with the right bit of code on a PIC16F micro, pressure on the touchscreen can be translated into X and Y coordinates. Using the PIC was a great choice in this instance: it’s possible to multiplex ports on an ADC pin with a PIC, making the entire system extremely efficient and easy to calibrate.

After that, it’s just a matter of plugging the output of the microcontroller into the touchpad connector of the MSX and writing a few lines of BASIC to draw a point on the screen. Video below.

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