While you’re not likely to see this technique used very much today, there’s a lot you can do with a 555, some logic chips, and a handful of diodes. [Fran] is here with a great example of using these simple parts to build a circuit that counts to zero, using parts you can probably find under your workbench.
[Fran] was inspired to build this diode counter from one of [Dave]’s Mailbags and [Colin Mitchell]’s 555 circuit book. The 555 is the standard component found in every parts drawer, but since we have tiny microcontrollers that cost the same as a 555, we’re not seeing the artistry of a simple timer chip and a few logic chips much these days.
This circuit began with a 555 attached to a 4017B decade counter. Simply by tying a few LEDs to the output of the 4017, [Fran] made a bunch of LEDs light up in sequence. Cool, but nothing unexpected. The real trick uses a few diodes and six LEDs to build a scanner – a line of LEDs that will blink from left to right, then right to left. Impressive, and with a little more circuitry it’s a Larson Scanner, as seen in Battlestar Galactica and Knight Rider.
The real trick for this technique comes when [Fran] pulls out a piece of protoboard, several dozen diodes, and seven old transistors to have a seven-segment display count from zero to nine. The 4017 simply counts out on ten pins, and each of these pins is wired to a bunch of diodes for each segment in the display. Add in a few resistors and a transistor, and [Fran] replicated what’s inside a seven-segment driver with discrete parts.
If counting to zero isn’t enough proof that you can do a whole lot with some diodes and logic chips, how about programming an Atari 2600 with one?
Continue reading “Diode Steering and Counting With A 555″
This beautiful instrument of musical delight is called the Zenotron, and it was built by [Mike Walters] for his friend [Zeno] in exchange for some keyboards. The Zenotron is the latest musical hack in a long line of awesome from the same guy who built the Melloman, its successor, the Mellowman II, and Drumssette, a programmable sequencer.
The sweet sounds of those babies all come from tape loops, but the Zenotron is voiced with a modified [Bleep Labs] Nebulophone synthesizer. Instead of the Nebulophone’s pots controlling the waveform and arpeggio, he’s wired up a 2-axis joystick. He left the LFO pot wired as-is. When it’s turned all the way down, he’s noticed that the joystick takes over control of the filter. [Mike] fed the audio through a 4017 decade counter and each of the steps lights up an array of four to five of the randomly-wired 88 LEDs.
[Mike] made the case from the top half of a small filmstrip viewer and an old modem, which is way better than the Cool Whip container housing we made for our Nebulophone. He re-purposed a toy keyboard and made a contact board for it with small tactile switches. This results in nice clicky feedback like you get from mouse buttons.
Of course there’s a demo video. You know the drill.
Continue reading “Zenotron: the Looks of a Kaypro II with the Soul of a Nebulophone”
[Shane Burrell] decided to spend some time learning how the keypad on the his Kenwood TM-710A APRS radio mic works. It uses a different technique than you might think. Normally a grid of buttons is scanned as a matrix to detect keypresses, but this hardware actually counts pulses on a serial wire to take each reading.
The stock radio sends a steady digital pulse to the handset and with each pulse the mic pulls the line low. It then uses a 4017 decade counter to see what comes back. If the edge count matches it means nothing is pressed, but a change in the number of pulses returning to the base unit can be used to extrapolate which button has been pressed.
[Shane] went on to implement this control technique using an AVR chip in place of the radio base unit. He used the data gained from measuring the pulse behavior using an oscilloscope to write the firmware for the project. He filmed a bit of a demo after the break which shows his findings.
We’re not quite sure how this would translate into your own home-brew projects, but the thought of scanning a keypad with two pins of a uC is quite desirable. Sure there is the 555-timer frequency technique, but we’re always down with new ideas.
Continue reading “One wire reads the keypad from the APRS radio mic”