Nuts & Volts - July 2005

Tech Forum

QUESTIONS

I recently acquired about 20 four-channel 29 MHz radio-controlled cars and when used as-is, they range as far as 30ft indoors. After slight mods, still good range, but once I install it in my car, the range becomes inches. Why is this? Does the car just block/ absorb that much of the signal?

#07051 Kevin Harris

St. Louis, MO

projects, without the need to construct the remote control itself. I'd think other experimenters could utilize such a receiver to add remote control capability to their robotic and other electronics projects. I suppose I could try to salvage this circuit from an old TV or VCR, but since I'm not interested in having a tuner for TV signals, I was hoping for a simpler circuit. I'm also looking for a good book on how to troubleshoot these circuits in various TV and VCR applications.

#07052

came with Mac software to download the pictures. I have been puzzled that I can't transfer pictures directly from the SD card, although I can download through the camera.

I recently bought a new three megapixel version for a friend and haven't been able to download pictures to my Mac. The CD that came with it (16-3844) seems to only have Windows drivers. I tried to use the driver from my old Flatfoto 1.3, but it doesn't work. I also tried to access the SD card and that doesn't work either.

RadioShack has been no help. Ideas anyone?

#07053

Dave Millville, NJ

I want to build a receiver circuit for a TV remote control. With the number of cheap "Universal" remote controls that are available, I'm hoping to be able to use one of these to control some of my electronics

Dwight Johnson Booneville, MS

A couple years ago, I bought a Flatfoto 1.3 Megapixel camera. It

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I have a number of IF transformers with no color-coded leads, and the primary and secondary have similar DC resistance. How can you determine the primary from the secondary, specifically the plate (collector) from the grid (base) leads?

#07054 Richard H. Abeles via Internet

I'm using motor controllers with LMD18200 amplifiers in a robotics project, and the amplifiers literally blow up if the motor power is reversed! I'd like to find a simple way to protect from reverse polarity, but without an inline diode or rectifier because of the voltage drop associated with diodes, especially at higher currents when the motor really needs all the voltage it can get. I've been thinking of using a relay powered by the motor power source (usually a battery), but since my motor battery, can be anywhere from 6 to 24 volts there could possibly be too much or too little voltage to run the relay coil.