Fab Lab Rwanda · Group work
Output Devices
Our group measurement method compares the electrical input power of an output device across defined operating states. A servo and a display are useful candidates because their loads behave differently, but each result must come from the actual connected device.
Measurement boundary
We will identify the device, driver if present, supply and controller before measuring. The power boundary matters: a measurement at a shared supply includes every load connected there. To report device power, the measured branch must be identified.
For a steady DC load, P (W) = V (V) × I (A). Current must be converted to amperes before multiplication. If voltage and current change significantly, multiplying two unrelated display averages does not establish instantaneous or average power.
Wiring the instruments
Voltage is measured across the device supply. Current is measured in series with the intended supply branch, using the meter's appropriate input and range. We will power down before changing the wiring, check the meter's rating and fuse, and restore the normal voltage-probe connection afterwards. A current-range meter must not be connected directly across the supply.
For pulsed loads, a suitable current probe or shunt measurement with a compatible oscilloscope setup can reveal changes that a handheld meter misses. The record should state the measurement bandwidth and whether a value is a steady reading, an average or a captured peak.
Operating states to compare
| Candidate | Defined states | Context needed |
|---|---|---|
| Servo | Powered idle, commanded motion, holding a known load | Supply at the servo, travel command, load and measurement method. Do not infer stall current from a normal motion reading. |
| Display | Backlight/output disabled and enabled, with controlled content | Module/driver identity, brightness and whether its controller is included in the measured branch. |
We will repeat each state under the same supply condition and retain the actual voltage/current readings. Any power calculation should refer to those paired measurements.
Applying the result to the plotter
The plotter design includes an SG90-type pen-lift servo. Its eventual power test should use the actual purchased unit and the printed lift mechanism, because servo variants and mechanical loading can change the current demand.
The controller plan describes the intended interfaces. It does not provide measured servo power or prove that the supply is adequate. Those decisions should follow the physical measurements.