Printing Text with a Chart Recorder

A chart recorder printing 'Hello World'

Chart recorders are vintage devices that were used to plot analog values on paper. They’re similar to old seismometers which plot seismic waves from earthquakes. The device has a heated pen which moves across a piece of thermally sensitive paper. This paper is fed through the machine at a specified rate, which gives two dimensions of plotting.

[Marv] ended up getting a couple of discontinued chart recorders and figured out the interface. Five parallel signals control the feed rate of the paper, and an analog voltage controls the pen location. The next logical step was to hook up an Arduino to control the plotter.

However, once the device could plot analog values, [Marv] quickly looked for a new challenge. He wanted to write characters and bitmaps using the device, but this would require non-continuous lines. By adding a solenoid to lift the pen, he built a chart recorder printer.

After the break, check out a video of the chart recorder doing something it was never intended to do. If you happen to have one of these chart recorders, [Marv] included all of the code in his writeup to help you build your own.

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The Disintegrated Op Amp

741By now we’ve all seen the ‘Three Fives’ kit from Evil Mad Scientist, a very large clone of the 555 timer built from individual transistors and resistors. You can do a lot more in the analog world with discrete parts, and [Shane]‘s SevenFortyFun is no exception: it’s a kit with a board, transistors, and resistors making a very large clone of the classic 741 op-amp, with all the parts laid bard instead of encapsulated in a brick of plastic.

[Shane] was inspired by the analog greats – [Bob Pease], [Jim Williams], and of course [Bob Widlar], and short of mowing his lawn with goats, the easiest way to get a feel for analog design was to build some analog circuits out of individual components.

[Shane] has a few more kits in mind: a linear dropout and switching regulators are on the top of the list, as is something like the Three Fives kit, likely to be used to blink giant LEDs.

A Motion Activated AC Switching Circuit using Mostly Discrete Components

AC motion switch

If you’ve ever dealt with a brightly lit Christmas tree, you might understand the frustration of having to crawl underneath the tree to turn the lights on and off. [brmarcum] feel’s your pain. He’s developed his own motion activated AC switching circuit to turn the lights on and off automatically. A motion sensor ensures that the lights are only on when there are people around to actually see the lights. The circuit also has an adjustable timer so [brmarcum] can change the length of time that the lights stay on.

The project is split into several different pieces. This makes the building and debugging of the circuit easier. The mains power is first run through a transformer to lower the voltage by a factor of 10. What remains is then filtered and regulated to 9VDC. [brmarcum] is using a Parallax PIR sensor which requires 4.5V. Therefore, the 9V signal is then lowered once more using a voltage divider circuit.

When the PIR sensor is triggered, it activates the timer circuit. The timer circuit is driven by a 555 timer. The circuit itself was originally borrowed from a classic Forrest Mims book, though it was slightly modified to accommodate the PIR sensor. The original push-button trigger was removed and replaced with the signal from the PIR sensor. The only problem is that the circuit was expecting a low signal as the trigger and the PIR sensor outputs a high signal. [brmarcum] resolved this problem with an NPN BJT to invert the signal. Once the timer is triggered, it flips on a relay that allows the mains electricity to flow through to the lights.

[brmarcum] soldered the entire circuit onto a piece of protoboard. The final product was then mounted securely inside of an insulated plastic case. This allows him to mount the circuit safely underneath the Christmas tree skirt. The PIR sensor is kept external to the enclosure and wired up into the tree itself. This allows the sensor to still detect motion in the room while the rest of the circuit is hidden away.

[via Reddit]

Analog Shield and PCB Quadcopter


We spent a little bit of time at the TI booth at Maker Faire to film a pair of interviews. The first is with [Bill Esposito] who is grinding away on his PhD. at Stanford. He’s showing off an Analog Shield for Arduino. He describes it as “an attempt to bring the analog bench to an Arduino shield”. We think this is a fantastic idea as most who are learning digital electronics through Arduino have little or no experience with analog circuitry. This is a nice gateway drug for the concepts.

The analog shield has a supply good for +/- 7.5 volts, 4-channel ADC, 4-channel DAC, and gets 100k samples at 16-bits. He showed us a spectrum analyzer using Fast Fourier Transform on the incoming signal from a microphone. He also built a function generator around the shield. And finally a synthesizer which plays MIDI files.

In the second half of the video we take a look at [Trey German's] work on a PCB-based quadcopter. His goal is to reduce the power consumption which will equate to longer flying times. To this end he chose the DRV8312 and a Piccolo to control each sensorless, brushless DC motor. The result should be 10% lower power consumption that his previous version.


Electronic Puzzle Box Uses Only Discrete Components

Puzzle box

Do you need an idea for a fun do it yourself gift for a friend or significant other? Look no further, [conductance] has you covered. He put together an awesome electronic puzzle box using all analog electronics. The puzzle case is shaped like an over sized die and is made out of wood. It also requires a small jumper cable and an external magnet to complete the puzzle.

This is a six-sided die, where each side has something different to offer. The “five” side of the die shows the progress you’ve made in completing the puzzle. Each of the five dots contains a green LED that will light up when the corresponding puzzle has been successfully completed.

The “one” side is completed by placing the included magnet over the dot. The magnet activates a reed switch which lights up the first LED. The “two” side contains a tilt switch. In order to solve this piece of the puzzle you must ensure the two side is facing up, as if you rolled a two. The “three” side contains three key switches. Each switch must be turned to a particular orientation. Once all three keys are configured properly, a third LED lights up.

The “four” side contains four sockets that fit the included jumper cable. This puzzle is solved by jumping the two correct sockets together. Finally, the number “six” side just has six momentary push buttons. All six buttons must be pressed simultaneously in order to light up the final LED. The tricky part is pressing all six buttons while simultaneously “rolling” a two in order to ensure the tilt switch is also activated.

Once all five LED’s are lit up, a relay is triggered which then activates a solenoid. The solenoid unlocks the door and reveals the prize. It’s always great to see electronics circuits like this that use all discrete components. This could have been accomplished any number of ways, but there’s something satisfying about a simple circuit that’s just right for the job. Be sure to check out [conductance's] schematic if you want to see how this puzzle works.

[via Reddit]

Heroes of Hardware Revolution: Bob Widlar

Bob Widlar (1937-1991) is without a doubt one of the most famous hardware engineers of all time.  In fact, it would not be an exaggeration to say that he is the person who single-handedly started the whole Analog IC Industry. Sure, it’s Robert Noyce and Jack Kilby who invented the concept of Integrated Circuits, but it’s Widlar’s genius and pragmatism that brought it to life. Though he was not first to realize the limitations of planar process and designing ICs like discrete circuits, he was the first one to provide an actual solution - µA702, the first linear IC Operational Amplifier. Combining his engineering genius, understanding of economic aspects of circuit design and awareness of medium and process limitations, he and Dave Talbert ruled the world of Analog ICs throughout the 60s and 70s. For a significant period of time, they were responsible more than 80 percent of all linear circuits made and sold in the entire world.

Bob Widlar


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A Video Vectorscope Oscilloclock

Tek 520A Oscilloclock

Back in the days of analog TV, vectorscopes were used to view video signals. [Aaron] has taken an old Tek 520A NTSC vectorscope and converted it into his newest oscilloclock.

The scope was originally designed to look at the signal provided by composite video. It draws vectors on a polar plot. By using test patterns such as color bars, you can ensure equipment is creating the correct color output. These scopes were so commonly used that many digital systems still provide a simulated vectorscope for color analysis. Vectorscopes were designed to be left on constantly, which is a good quality for a clock.

[Aaron] has a history of converting oscilloscopes into clocks, which we have featured in the past. This build is similar, using his custom control hardware to drive the display. Since analog vectorscopes are pretty much obsolete, you can find them on eBay at low prices, so these oscilloclocks could be relatively cheap to build.

In the write up, you get a teardown of the Tek 520A, showing the modifications made to build the clock. After the break, check out a video of the Tek 520A Oscilloclock.

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