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Recent Questions

July/August 2018

Smooth LEDs?

What makes some LED replacement bulbs dimmable, while others are not? Some of the replacements I have purchased do not dim very smoothly. They seem to dim in steps and then just turn off before lowering to where I need them to be. The previous incandesants dimmed much more smoothly down to a soft glow. Is there a different, (maybe more expensive) type/technology that  would more closely emulate the incandesants? I'm using an X10 controller for the dimming, could this be the problem?

Everett Barham
Elvaston, IL

TV Image Capture

What’s the best way to capture images from my TV? I’m looking to do something like a computer “print screen.”

Sharon Fitzgerald
Chattanooga, TN

Phone Line Intercom

We use our cell phones as our main phone service, so our “land line” is no longer being used. Is there a way to use the house phone wiring along with the old phones as a whole house intercom system? I have a detached garage/workshop away from the house where this would be especially useful, not to mention almost every room is wired. Would I need to disconnect from the phone company "grid" to do this?

Jay Bousquet
Lexington, NC

Show Me The Power

When renovating houses as a hobby, I need to locate powerlines inside the walls and also underground. What curcuit can I build that would be useful? Also, what is the theory of how such a detector would work?

Denzel Meier
Winnsboro, SC

PCBs With PTHs

Is there a hobbyist method for making circuit boards with plated through holes at home? Also curious by what is meant by multilayer boards. I'm just getting started, so forgive if this is an obvious newbie question.

Leonelo Márquez
Maplewood, MN

May/June 2018

PS2 Emulation

My Sony CD changer has a PS2 keyboard port to enter the CD title, details, etc. Instead of typing, is there a way to emulate a PS2 interface on a PC or processor board to automate the key presses?



I have successfully plugged an old PC keyboard into that CD changer to enter data. However, what is it that you want to automate? Every entry i.e. artist, titles, etc.; are different?

M. Herman

Yes, you can emulate a PS-2 keyboard. An SPI-master port will do the job as long as it can handle 11 bits, or two 8-bit values in rapid succession. Not all microcontrollers can. (If you lack a good SPI port, emulate it in software.) Use the MOSI signal for the key-code transmissions and use the SCLK signal to emulate the keyboard’s clock output. The bits transmitted when you press a key look much like those put out by a standard UART: a start bit, eight data bits, an odd-parity bit, and a stop bit.

The keyboard’s clock output produces a logic-1 in its idle state and created a positive edge for each of the 11 bits. An SPI port configured as CPOL=1, CPHA=1, provides the proper timing. Note: The least-significant bit of an 8-bit key value gets sent first. My old PS-2 keyboard produces clock signals at 13.7 kHz. That’s a good frequency to start with for the SPI port.

A PS-2 keyboard assigns a unique non-ASCII code to every key. Find a list of the keys and assigned codes here: When you press the “A” key, for example, the keyboard’s circuit produces the hex code 1C. When you release the “A” key, the keyboard transmits a key-release code F0, followed by the key’s code again.

The shift key works the same way. To send an uppercase “A” your microcontroller or processor board would send the SHIFT-key code, the A key code (then a short delay) followed by the key release code and the A key code again. Then it would send the key release code followed by the shift-key code.

Remember, your code must calculate an odd-parity bit and insert it in the 11-bit value to send. You can find parity-generator code on the Internet. Also, ensure you send the key and release values in bit-reversed form. Thus, the 1C code (0001 1100) for “A” must get transmitted as 0011 1000. You can simply set up your code so it uses the “reverse-bit” values to start with.

Jon Titus
Herriman, UT

Proper Motor Selection

I need some tips on selecting motors for an art project that continously rotates five different circular platforms (10” diameter, 15 lbs) 360° in one direction, then in the reverse direction. The complete rotation of each platform should take approx 30-40 seconds (not critical). A direct drive approach would be preferred (seems simpler), but I could use a gear reduction scheme if it were more cost-effective.

Caitlin Russell
Stony Creek, VA

No Wi-Fi For The Pi

How can a Raspberry Pi be made to talk to IoT devices over low power FM rather than Wi-Fi? Looking for distances under 100 ft.

Durriyah Shamoon
Eau Claire, WI

New Life For Magnets

Has anyone tried to revive permanent magnets that have weakened over time? What is the best method? Can they be made “good as new” or is it better to just replace them?

Petrina Martinec

Measuring Heat With Crystal Diodes

I have a bunch of crystal diodes in my junkbox that I want to use to measure heat. I seem to remember a circuit for it some years back that I’m trying to reconstruct from memory. It’s not working very well, so I must be missing something. Anyone have a simple circuit or explanation of how it should work?

John Marion
Bend, OR

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