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You can use a small adjustable supply to check whether a battery-powered device turns on without carrying all its battery sizes. Make:’s DIY project uses a 9V battery or a 12V battery pack as its input, then lets you adjust the output to suit the device. It is intended for a brief functional check—not as a proven replacement for the device’s batteries or a general-purpose bench supply.
What the pocket-sized supply is for
Jason Poel Smith’s Make: project addresses a simple problem: testing several battery-powered devices can mean carrying multiple battery types and combinations. The project aims to power a device long enough to see whether it works, using an adjustable output instead of its normal batteries. Make: project description
The described inputs are a 9V battery or a 12V battery pack. You adjust the circuit’s output to match the device, then attach the output wires to the end terminals on the device’s battery connector. That description does not establish that every battery-powered device is compatible; matching voltage alone is not enough to confirm a safe connection.
Parts and tools listed for the project
Make: names these components and tools:
- Perfboard
- One 9V battery connector
- Seven 270-ohm resistors, preferably 1/8 watt
- Two alligator-clip wires
- One LM317 adjustable voltage regulator
- One 220-ohm resistor
- One 1 µF capacitor
- One 0.1 µF capacitor
- One 8-position DIP switch
- A soldering iron and solder
The accessible project text lists these materials but does not provide a complete schematic in that text. Consult the full project instructions and confirm the circuit wiring before building it or substituting parts. Make: project instructions
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Set up a device check carefully
- Identify the device’s requirements. Check the battery compartment or device documentation for the required voltage, battery arrangement, and polarity. If you cannot establish these, do not connect the supply.
- Build and inspect the circuit using the complete instructions. The parts list alone is not enough to determine how the components should be wired.
- Connect the intended input source. The project description specifies a 9V battery or a 12V battery pack.
- Adjust and verify the output before connecting the device. Check both voltage and polarity at the output; do not rely only on a switch position or assumption about the wiring.
- Connect to the battery terminals and observe the device briefly. Stop if it behaves unexpectedly, becomes warm, or the circuit shows signs of distress. A quick test is not proof that the device will operate normally under extended use.
What the LM317 specifications do—and do not—tell you
Texas Instruments describes the LM317 as an adjustable three-pin positive-voltage regulator with a specified adjustable output range of 1.25 V to 37 V and output current up to 1.5 A under specified operating conditions. Its datasheet also describes current limiting, thermal-overload protection, and safe-operating-area protection. These are specifications for the regulator component, not measurements of the assembled Make: project. Texas Instruments LM317 datasheet, revision Z (April 2025)
Make: does not state the assembled circuit’s measured output range, current capability, or test results. The component’s maximum ratings therefore do not show that this particular build reaches 37 V, supplies 1.5 A, or can power a specific device. The finished circuit’s performance depends on its design, input source, load, and thermal conditions.
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When not to use this project
- Do not connect it to a device unless you have verified the required voltage and polarity.
- Do not assume it can replace a battery pack just because the nominal voltage appears to match; the project description provides no measured current capacity or broad compatibility list.
- Do not use it to power an irreplaceable device until you have checked the complete wiring and independently verified the output.
- Do not treat the regulator’s datasheet ratings as performance figures for the finished supply.
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