Component tester
Three sockets. Push two or three legs of an unknown part into them in any order and it names the part, measures it, and tells you which leg is in which socket.
It is the instrument a drawer full of loose parts asks for, and the one a beginner can least afford: a transistor's legs are not marked, an electrolytic that has lost its stripe has no polarity on it, and a resistor whose bands you cannot read is a resistor of unknown value.
Pins
| Pin | What it does |
|---|---|
1, 2, 3 |
The three sockets. Any two or three of them, any way around. |
A two-legged part leaves one socket empty; that is what a tester with a resistor in it looks like, and neither the netlist warning nor the audit treats it as a wire forgotten.
What it names
| it says | and measures |
|---|---|
RESISTOR |
the value, from about an ohm to 1 Mohm, and which two sockets |
CAPACITOR |
the value, 0.1 µF to 500 µF, and which two sockets |
DIODE |
the forward drop and the current it was measured at, and which socket the anode is in |
LED |
the same, when the drop is too big to be a plain silicon junction |
NPN / PNP |
hFE, Vbe, and which sockets the base, collector and emitter are in |
N-MOSFET / P-MOSFET |
Rds(on) at 5 V on the gate, and which sockets the gate, drain and source are in |
How it measures
Twenty-four phases of 5 ms, and then it names what it found and starts again, a hair over a tenth of a second for a whole identification.
Twelve pair phases, four for each of the three pairs of sockets: a settling phase, a forward drive, another settling phase, a reverse drive. Each drive is 5 V behind 4.7 k, and each is measured twice, half way through and at the end. Two readings rather than one is what makes a capacitor a capacitor: a voltage still moving when the phase ends is the only thing in this instrument measured over time rather than at rest, and its value comes out of the first-order response rather than out of an assumption that the ramp is straight.
Twelve active phases, four for each socket taken as the control: the control driven through 10 Mohm, one of the other two driven through 4.7 k, the third as the return, in both polarities and with the other two sockets each way around. A part that conducts between two terminals only when the third is driven is a transistor, and which of those twelve phases turned it on says which terminal is which.
The control resistor is ten megohms on purpose: a base driven through a few kilohms saturates the transistor, and a saturated transistor's collector current is a measurement of the collector resistor rather than of the gain.
It measures; it does not ask
Nothing in here looks at the netlist or at what part is wired to the sockets. Which means it can be fooled in the same ways a real tester can: one part at a time, because two parts across the sockets at once is one part it cannot name; a resistor across a transistor's junctions is a resistor; and a part with a leg not in a socket is whatever is left of it.
What it cannot be wrong about is the physics, and that is the honest caveat. A real
tester on a real 2N3904 measures a device that is hotter than its datasheet, has leakage,
and disagrees with the next one out of the reel. This one measures Mokxi's Ebers-Moll
model card, so the hFE it shows is the beta that card was given, seen through one
operating point, a few percent over the card's own number, because the Early effect is
in the model and the measurement is taken at a real collector voltage. The reading is
a measurement of a model, not of a part.
What it does not model
No inductance: measuring one needs an AC source this does not have. No ESR, no leakage and
no dielectric absorption on a capacitor, because the model of a capacitor here has none
of them either. No MOSFET threshold voltage. The gate is driven to one level rather than
swept, so what comes back is the on-resistance at 5 V on the gate and not Vgs(th); and
Rds(on) is measured through a 4.7 k load, so it is quoted to about a twentieth of an
ohm and a part well under that reads near zero. No Zener voltage, because it tests at
five volts and most Zener knees are above it: a Zener reads as an
ordinary diode here.
Capacitors under 0.1 µF go to the multimeter's capacitance range instead, which reaches down to a nanofarad, and the face says so.
See it in action
What is this part? has two testers, one with a transistor and one with an LED. Drag anything else across the sockets. See also the bench instruments.