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Recent Questions

2022 Issue-2

Temperature Sensing LEDs

I’m looking for a temperature sensing circuit that will light each of three LEDs at approximately 80°F, 90°F, and 100°F.


Component Footprints

Can someone please explain the standards for the footprint of electronic components? I’m trying to figure out the best way to lay things out on a circuit board. I’m new at this and any advice would be appreciated.


Good Timing

I have an old model automotive timing light that attaches between the #1 spark plug and wire. How can I make an inductive pickup to sense the signal so I don’t have to detatch the wire? Is it even worth trying to convert?


Proximity Detector

I want to build a backup proximity detector like many newer cars have, as a fun useful project. The type that beeps in reverse when something is behind my car; faster beeping means the object is closer. I’m new to electronics and I need help designing the circuit.

I thought of using the PING))) sensors available from Parallax to sense the distance to objects. Any help with the circuit is welcome. It would be preferred to have it auto-activate when in reverse, but I could just as easily flip a switch mounted next to the shifter to activate if it becomes too complex.


Three-Way LED Flasher

I need a simple circuit to sequentially flash three separate strings of 10 LED lights. Flashing two strings is easy; three is tougher.


Motor Brake

I’m looking for a schematic for an electronic brake for a one phase 120 VAC motor. I had a commercial one, but it failed. I discovered it was potted with no way to tell what was inside.


Resonator Frequency

I have in my junkbox what I believe to be ceramic resonators. What is the best way to test them to determine their frequency?


Laser Eye Protection

With high powered laser prices dropping like crazy, I decided to pick up a 3W blue laser from eBay for $50 to experiment with. I’m concerned about eye damage and would like some advice on eye protection. What makes a pair of laser goggles good and what should I stay away from?



First you are correct in assuming you'll need protective eyewear. I've worked with high powered lasers, even higher than 3W, but the most important thing is to be sure the goggles cut out as much LASER light of the incident frequency as needed to protect your eyes. Understand that no goggles can be made to cut out enough directly incident laser light to protect your eyes for long.

Blue light is in the higher energy light range and if you pick the opposite color eyewear it will protect your from the blue light, meaning select red filters. Then, if you really want to be thorough, measure the light getting through to be sure it's below the eye damage threshold. I'm sorry but I do not know that level and you haven't specified the light wavelength or frequency. I did a quick search and found this link on Amazon: Tactical-Flashlight-Travel-Camping-Outdoor goto Amazon then tack on this: "/dp/B0B4KKHXS7" to the URL to get to the link I'm trying to provide

You will also notice that this is a responsible company that also includes eye protection, and guess what, the lenses are RED. Also notice they do not say this is a blue LASER. SO if you can send me the link to the one you purchased I'll do some research but you can at least ask the seller what they recommend for eye protection.

Philip Karras
Mount Airy, MD

2022 Issue-1

Arduino Clone - Yes Or No?

My daughter is preparing for a science fair. Each participant is limited to a total of $50 for parts and supplies. Central to her project is an Arduino Uno. I’m tempted to order a half-priced Chinese clone from eBay vs. an authentic model from one of the domestic supply houses. Is there a downside to using one of these inexpensive clones or are they identical to the real thing?

Diogo Alves
Saint Charles, MO

Adding Aux Input To Stereo

My car stereo boasts an AM/FM radio and a cassette player (2007 model. My smartphone, however, has all my stored music, Pandora, Amazon music, and even Satellite radio. There is no auxilliary jack or Bluetooth to connect my phone to the car stereo like with new units.

Is there a way to tap into the cassette deck circuitry and add an aux jack to use my phone as an audio source? Would I need a preamp or other circuit to create an interface or just a direct connection at some point inside the stereo?

Gilberto Onio
Framingham, MA


Before you get out your tools and start digging around your cassette player, the good news is there is an easier way! It’s lucky that you are interested in connecting an audio source to a cassette player rather than to a CD player! Years ago, in the heyday of cassette systems, a ‘cassette adapter’ was widely available. This was simply a cassette shell with a magnetic head inside, just like a player’s tape head. This adapter was inserted into the player, like any cassette, and its cable was plugged into the stereo output of whatever you desired. The head in the adapter magnetically coupled the audio to the player’s head and in most cases, it played quite well.

The better news is they are still available, Amazon, eBay, Walmart and many others still list them at around $5 plus any shipping. Maybe, if you have a junker cassette unit or parts, you may be able to DIY an adapter but I don’t know if the cassette player head impedance is different in the adapters,or if that would make any difference. I don’t think this concept presents any harm to the cassette player.

But, is it all really worth the effort to save $5?

Len Powell
Finksburg, MD

My 2002 Subaru doesn't have any "modern" connections either. The simple solution was an Ion Audio Cassette Adapter. It's basically a cassette tape case with the electronics for a Bluetooth connection inside. A short, flexible wire sticks out of the player for the antenna. This particular brand seems to no longer be available from Amazon, but search "bluetooth audio cassette adapter" for other options.

Rick Gregory
Salt Lake City, Utah

There are two was to do this easily, without doing any mods to the circuit.

  1. Buy an FM radio transmitter that plugs into your device & then transmits to the FM radio in your car. There are many different ones to choose from on Amazon & eBay; search on, "Bluetooth FM Transmitter for car" will only show the Bluetooth devices or "3.5 mm Stereo jack to FM transmitter" which will also find devices that plug into your phone/mp3 player with a 3.5mm stereo plug. It even found a Bluetooth transmitter!
  2. Buy a cassette that plugs into your device and send the audio to a magnetic head in the cassette that then passes that audio onto the magnetic head in the cassette player in the car. see: Arsvita-Audio-Cassette-Adapter-Auxillary/ at: https://www.amazon.com/dp/B07N2KPTGW
  3. Last, if you really want to take the radio/cassette player out and dig into it you probably can add a stereo port. The easiest way would be to find the stereo volume controls and add your input just before or after the volume control. NOTE: If you add the port just after the volume control you will have to change the volume with your device. If you add your input before the volume control then you'll be able to adjust the volume with your radio's volume control and with your device.

Phil Karras
Mount Airy, MD

Kurt Stefans
Valparaiso, IN

When I bought my first XM Radio in 2004, It came with a "cassette adaptor". It looks like a cassette tape with a cable and stereo plug (like the kind on your headphones). I never used it, so I don't know how effective it was. You might be able to find one on line. Most cars today don't come with cassette players so there may be a surplus of these out there.

Rick Drapala
Yuma, AZ

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