How to Construct a Digital Multimeter
Building a digital multimeter from a kit requires good soldering technique and attention to detail. Kit multimeters are accurate enough for most uses, and by calibrating the meter themselves, kit builders learn how to maintain that accuracy. These projects can be completed in a few evenings.
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Things You'll Need
- Soldering iron
- Rosin flux
- Eutectic solder
- Alcohol
- Cotton swabs
- Flush cutter
- Solder wick
- Tweezers
- Power supply
- Resistors for calibration
- Known good multimeter for calibration
Instructions
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Check that all the parts are present in any kit you plan to build. Follow the manufacturer's checklist carefully to ensure that all parts are in the package. Verify that resistor color codes, capacitor part numbers and integrated circuit part numbers match up with the parts list. This serves a dual purpose: checking the parts and teaching the kit builder about standardized part nomenclature.
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Build the kit in sections according to the manufacturer's instructions. Work slowly and carefully to avoid later problems. Strive for high reliability solder joints. Always apply rosin flux before soldering as it cleans the metal parts and breaks down surface tension. Newer kits use lead-free solder that requires temperatures of 700 to 800 degrees Fahrenheit. Using flux and keeping the soldering iron tip clean are key. Touch the iron to the parts and watch for a quick color change to bright silver, then feed the solder into the joint. Once it fills the joint, remove both the solder and iron.
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Clean excess flux from the board with alcohol and cotton swabs. When you install the display, clean its edges with alcohol and clean the zebra connectors, too. These connectors are common in displays. They look like black rubber rectangles, but they consist of parallel conductors. Fingerprints will interfere with good contact, so once they're clean handle them only with tweezers.
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Calibrate the meter per the manufacturer's specifications. Some use a variable power supply as a standard. Others use a power supply and a pair of resistors as a voltage divider. The kit meter has a trim pot -- a variable resistor -- that adjusts the calibration. Use a small screwdriver to turn it. Do not press down on the trim pot as it is fragile.
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Tips & Warnings
Building a multimeter kit rewards slow, careful work. Perform each step as detailed in the instructions, paying special attention to the quality of the soldering. Avoid partly filled solder joints or solder bridges.
References
- Photo Credit Polka Dot Images/Polka Dot/Getty Images
