Everything for Electronics

Unanswered Questions

Better Radio Communications November 2011

I’ve been a reader for some years, and electronics is my daily work. Now, I have to work with the Motorola PTP 600 radio. The system I am working now has three sets of PTP 600. They were set up the same way at three different locations to communicate to the main control hub. One of the stations has kept the connection pretty well since the first day, but the other two sometimes show slow or very slow data transmit. Looking at the status — as they are all set up with i_DFS — the link capacity sometimes drops to 20, the transmit in teens, and the vector error goes up positive. Please show me how I can get them to work  more stably. I am working in the war zone of Afghanistan!

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Single-Stroke AC Bell November 2011

We would like to operate a single-stroke AC bell that would ring once every time the phone rings in cadence. The telephone line power — 40 to 120 VAC at 15 to 60 Hz — should power the bell. We prefer no external power supply. A typical single-stroke bell has a coil voltage of 24 VAC drawing 0.5 amps.  Coil resistance is 10 ohms.

Michael Lenihan
Southampton, NY

Microcontroller Cards December 2011

I’m just getting started with microcontroller cards. What is the difference between an AVR microcontroller card and a PIC microcontroller card? I am interested in purchasing a course kit that includes the books and the microcontroller card for the course.

Steve Huff
Des Moines, IA

Stanley Garage Door Opener December 2011

Where can I get a schematic for the circuit board in my Stanley model 520 garage door opener? The circuit board has a burnt capacitor and I need to find the value to repair it.

Orlando Silveira
Toronto, Ontario

Speed Control Of A 3/4 HP 12 VDC Motor December 2011

I would like to control the speed of a 3/4 HP 12 VDC motor with a 3.3 VDC microcontroller. I've seen in past issues where PWM was used to control small DC motors but not fractional HP motors.

Can someone show a circuit to interface the high power motor with a low power MCU from a 12V auto battery? Presently, I'm trying to use a Freescale MC9S08QG8 MCU. Ultimately, I would like to use the motor as a brake, and then reverse rotation on a small flywheel for a few revolutions.

The motor goes the same direction all the time, just the flywheel will reverse direction.

Scotts, MI

S-KMS Recliner Chair September 2012

I’m trying to repair a microprocessor controlled massage chair, imported by HWE, Inc., Los Angeles. ID S-KMS mfg # 000101, additional number 61011-L.

NEC is the processor manufacturer and has indicated in thier product description that the processor is a uPD75004CU four-bit discontinued part. I am reasonably sure there is an onboard program, but do not know enough about it to get it into test mode.

It appears to be completely shut down. I have scoped the in and out, but there is no activity.

If the processor is dead, then a $1,500 item is junk, unless someone can help.

I would like to have a schematic, service manual, literature, or advice.

Martindale, TX

IC Identification September 2012

I'm attempting to repair a PC board for a RadioShack PT Cruiser remote control car. The IC (20-pin) has the following numbers printed on the top: S111g, KJET IC001, OU97112.

In the tech manual, the IC is identified as KS57C0301.

(1) Program memory is 1K byte (KS57C0301) and 2K byte (KS57C0302).
(2) Data memory is 128x4 bit (KS57C0301) and 256x4 bit (KS57C0302).

Parts from RadioShack are no longer available. Any help in identifying a substitute would be appreciated.

Tom Recker
Peoria, AZ

Programmable Equalizer September 2012

I want to design an inexpensive audio graphic equalizer that us older guys (and ladies) can use with our radio (ham) gear. What I envision is a programmable equalizer that can be programmed to boost frequencies based on hearing tests. Even better would be a stereo equalizer that can be used with a stereo headset to allow us old timers to hear better.

Jim Darrough
Springfield, OR

Differential Thermostat September 2012

Currently I am using two thermostats to activate an attic fan: one thermostat to determine a cool outside temperature and a second thermostat to determine the attic temperature. When the differential between the two reaches the set point of the two, they both turn on the attic fan, pulling cooler outside air up and through the attic. This only works when each thermostat reaches their "set" point temperatures. I would really like to be able to have the fan come on when a variable differential temperature — say 20 degrees — is reached, regardless of outside or attic temperatures; also, only if the attic temperature is warmer than the outside temperature.

Vonn Hockenberger
Livermore, CA

Wireless Water Level Monitor/Indicator September 2012

I'm looking for a schematic solution to wirelessly indicate the water level of a distant water tank more than 100 m away.

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