A papercraft resistor calculator from Adafruit

The Adafruit blog just posted a neat papercraft resistor calculator. If you haven’t yet learned the horribly offensive mnemonic for resistor color codes, now’s your chance to have a cheap and portable resistor value reference.

This papercraft resistor calculator is the latest in the family of Circuit Playground tools that include a fabulous electronic reference app we reviewed some months ago. Instead of an Android or iOS device, the papercraft resistor calculator runs on its own mechanical computer; a series of four printed disks and some paper fasteners.

If you’d like to print out your own resistor calculator, Adafruit put up the PDF on GitHub and posted the Illustrator file on Thingiverse for easy editing. It’s not the old-school cool of a slide rule, but we could easily see this resistor calculator being useful if you’re ever lucky enough to teach electronics to children. At least then you won’t have to share that offensive mnemonic.

Slowing a Bopit so the littles ones can play too

[Johnny Halfmoon] wanted to help out his three-year-old who was fascinated by the Bopit electronic game. In its stock condition it’s a bit too fast for the young one, so he cracked it opened and added the option to slow things down.

Above you can see the Bopit Extreme with the top half of the case removed. Although not hard to get open (there’s just 12 screws to remove) the spring-loaded appendages will fly apart when you do. He warns to pay attention at how they go back together.

There’s one axial resistor which affects the running speed of the game. [Johnny] desoldered this, replacing it with a circuit that toggles between that original resistor and a potentiometer. Now, one switch position allows for normal play, the other allows for adjustable speed based on the potentiometer position. Check out the results in the clip after the break.

Looking for some other fun electronic toy hacks? Why not try out this cursing Simon Says?

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Which resistor values should you order for all circumstances?

A hard drive crash, and some other happenings that aren’t entirely clear to us, led [Devbisme] to put in a parts order. As he wanted to make the most of his shipping costs, he decided to fill out the order with parts that he’ll use eventually. He’s been working with surface mount designs and wanted to move from using resistors with 0805 packages to the 0603. Having nothing on hand, he devised a way to account for almost all standard values with the fewest number of different resistors.

That’s a mouthful, but what he actually did was figure out what combinations of resistors can best be wired in parallel to achieve a different standard resistance value. This way, if he doesn’t have a specific value he can solder one 0603 surface mount resistor on top of another one to get there. He ended up writing a Python program to best calculate this set of values. It came up with a set that lets him synthesize 159 of the 168 standard resistor values within +/- 4% using just 19 actual resistor values. His method requires anywhere from one to three resistors to get to each value. Soldering three 0603 packages on top of each other might not be the most fun, but it makes for easy parts inventory management.

Ohm Sense makes sense of resistor color bands

[Alex Busman]’s first foray in iOS programming looks like a pretty useful tool. He came up with Ohm Sense, an iPhone app that will take a picture of a resistor and calculate the value based on the color bands. It’s a great tool that we wish we had when we were starting out. At 99 cents, the app is also much cheaper than the emotional cost of our relationship with Violet.

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Resistor substitution box

[Vincent] on the EEVblog forums had an idea for an inexpensive resistor substitution decade box.

The build uses cheap decimal thumbwheel switches he bought on eBay. Each switch is wired up with resistors for each digit, and each switch is wired up in series. The result is a small, easy to read resistor box with a range of 1 Ω to 10 MΩ.

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Dabbling with CPLD generated VGA signals

It seems like all the cool kids are leaving the 8-bit hobby microcontrollers in the parts bin and playing with more advanced parts like Complex Programmable Logic Devices. [Chris] is no exception to the trend, and set out to generate his own VGA signal using one of the beefy semiconductors.

It seems that he’s using the acronyms CPDL and FPGA interchangeable in his post but according to the parts list this setup uses an Altera EPM7128SLC84-7N CPLD. In order to generate the VGA signal he needed a way to convert the digital signals from the chip into the analog values called for in the video standard. He chose to build a Digital Analog Converter for the RGB color values using a resistor network which he calculated using PSpice. The other piece in the puzzle is a 25.175 MHz oscillator to clock the CPLD. As you can see after the break, his wire-wrapped prototype works exactly as designed. The example code generates the rainbow bars seen above, or a bouncing box demo reminiscent of a DVD player screen saver.

Want to know more about programming CPLDs? We did a tutorial on the subject a while back.

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Analog computer does math

This analog computer can multiply, divide, square numbers, and find square roots. It has a maximum result of ten billion with an average precision of 2-3%. [Miroslav’s] build recreates something he saw in a Popular Electronics magazine. It uses a resistor network made up of three potentiometers with a digital multimeter is an integral part of the machine. To multiply a number you set the needles on the first two knobs to the numbers on which you are operating. To find the result turn the third knob until the multimeter has been zeroed out and read the value that knob is pointing to. It seems much more simple than some of the discrete logic computers we’ve seen, yet it’s just as interesting.