The cool kids all file their resistors for accuracy

Here’s a tip to keep in your back pocket, you can use a metal file to adjust your resistors. [Gareth] shows off this technique in the video after the break. A metal file is literally all that you need to do some fine tuning. Just make sure you’re starting off with a carbon film resistor as this will not work with the metal film variety.

His example shows a 10k resistor which is reading just 9.92k on his multimeter. But he needs precisely 10k. After getting through the protective layer he makes just a couple of passes with a small file, each time adding about 20 Ohms of resistance. Now he does mention that excessive deep cuts can hurt the power rating of the resistor. But this certainly isn’t damaging it if done correctly. It turns out this is how they are tuned at the factory.

One possible use he mentions is trimming the balance on a hacked servo motor.

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A resistor’s fiery death used to launch fireworks

Check out this control center which [Awesome0749] built for launching fireworks. From the looks of his stash he’s going to be doing quite a bit of celebrating. The control console is clean and offers some safety features, and he just upgraded to an interesting ignition technique.

He’s using CAT5 cable to connect to the fireworks. At the top of the enclosure you can just make out the edge of the almond-colored wall plates which offer three jacks each. The two keys on the controller must be turned on to power the device. There is also a safety toggle switch in the middle.

The ignition is cause by running 70 VDC through a 1/4 Watt 24 Ohm resistor. As you can see in the demo after the break this results in flames quite quickly. One other thing we saw in the demonstration is that only the LED for the button which is hooked up comes on when the system is armed. We didn’t see a schematic, but he must have wired this so the system checks for continuity to ensure there’s something wired to the business end of the button.

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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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