Nuts and Volts - September 2008

>>>READER-TO-READER QUESTIONS AND ANSWERS

>>> ANSWERS

[#5083 - May 2008]

Has anyone hacked a digital camera and installed the sensor and minimum circuits into an old film camera like an old Nikon F or Leica M2 or M3? I've seen astrophotog guys hack a digital Canon EOS D30 and Rebel to remove the IR filter for IR photography ... I don't know which electronics I can safely clip out of the digital donor. (There are film camera nuts out there that would die to see this done.)

I’ve had little success taking apart digital cameras. I’m on my third (since 2001) and once they break I’ve tried to open the case out of curiosity. The internal circuits are tightly packed and use a lot of custom components that would be hard to use again.

A 35 mm mechanical film camera uses film at the lens focal plane to capture an image of 36 x 24 mm as described here: http://tinyurl.com/ ygss⁴j. However, the active imager in a digital camera is much smaller, typically 4 mm to 16 mm diagonal, as indicated here: http://tinyurl.com/ yx⁶q³s. Some form of relay lens would be required to convert the 35 mm size image to that of the salvaged sensor. This would not readily fit into the existing film camera outline, and would require access to precision machine tools for construction and alignment.

A brief history and description of digital camera resolution is given here: http://tinyurl.com/4j65sz. Overall, your project is not practical, but the digital camera technology is quite fascinating!

Peter Stonard Campbell, CA

[#6082 - May 2008]

Several years ago, I'd seen a device that plugged into a laptop's modem port and then to the headset port of a cell phone, and presto — an Internet connection! All that I can figure out is the interface device must have somehow produced a tone for the modem to believe it had a live line. From there, it was a simple matter of

pushing 'speed dial' on the cell phone and away you went — surfing. Do you have any ideas about this and how it could be built from scratch? Better yet, could there be something built that would handshake between the data or USB port?

What you are looking for is simply a cellular capable modem, which can be installed in parallel to your existing modem if it is not cellular ready. I used an IBM P/N 85H8059 FRU 38H5062 PCMCIA data/fax modem card on an older laptop which was cellular capable, but you need an adapter cable for the specific cell phone. You should be able to pick one up used or surplus for very little money. Look for Cellular Ready ("Spectrum Connected") on the back of the modem card. You will also need a PCMCIA port on your computer. It had a max speed of 33. 6 kbps, but I think there was also a faster, later one at 56 kbps from IBM.

Walter Heissenberger

Hancock, NH

[#7081 - July 2008]

My furnace/air conditioning servicer recently replaced the control unit in my high-efficiency furnace. The defective portion of the control unit turned out to be the spark generator, but, in the process I see the unit has a single-wire electric flame sensor, not the old standard thermocouple. I can't figure out how the thing works. Can someone please enlighten this old-timer?

In the old days of gas heating appliances, a pilot flame was used to start the main burners when heat was required. Typically, this pilot was started by a match or a spark generator. A thermocouple was used to check for the presence of the pilot flame by detecting its heat. If the thermocouple failed or did not detect heat, the main burners would not fire.

In today's energy conscious times, standing a pilot 24/7 to light the main burners is a waste of fuel. To save energy, appliance manufacturers now wait for a demand for heat, light the pilot flame, check for a pilot flame,

and then open the main burner valves. Some schemes don't have pilots and directly spark the main burners. In either case, detection of a good flame is the key to safe burner control.

The single wire detection method is viable because a flame acts like a diode electrically. By expressing low voltage AC across the sense wire and detecting half wave rectification, the ignition module can deduce the presence of a good flame. Some ignition modules use the high voltage spark wire as the sense wire thus eliminating the need for a separate flame sense wire. The secret here is the flame is a diode. No flame, no diode, no rectification, no heat, and hopefully no raw gas vapor in your cellar.

John P. Gardner Franklin, NH

[#7082 - July 2008]

Can a security system be built that would utilize a switch on a door to trigger a cell phone to call a number? A similar system on the Internet costs around $300. Can something be built for less than $100 with a “pay as you go” wireless phone?

Cellular phone electronics can be purchased as modules, for “m2m” (machine to machine) links over the cellular phone network which allows construction of hobby projects. For example, the GM862 made by Telit and sold through SparkFun Electronics ( www.sparkfun.com).

A GSM SIM card is required to activate the phone which uses AT style modem commands for control and will send and receive data streams, SMS text, voice, or data up to 57. 6 kbps. The module is compatible with standard international GSM cellular phone bands and SIM carriers in the USA (AT&T, Cingular, and T-Mobile). For a switch closure activated alarm, the GM862 will only need a simple microcontroller and a power supply. The module sells for about $150.