Blinky Hawk User Guide

Three answers instead of one ambiguous zero

A normal voltmeter reading 0 V can't tell you whether you're on a genuinely connected net, or simply not touching anything — a floating probe, a clip that fell off, an open relay. Blinky Hawk resolves that ambiguity continuously:

It works by briefly interrupting an internal resistor bridge and watching how the resulting microsecond transient decays across the probes — high impedance decays slowly (open), low impedance decays fast (closed). The injected signal is tiny (never more than ~1.25 V behind hundreds of kilohms, worst-case ~6 µA), your meter stays in voltmeter mode the whole time, and detection runs many times per second. Full technical background is on the main project page.

One switch: power, isolation, and a test load

The toggle is a triple-pole, three-position switch with a center-off. One pole switches the battery; the other two galvanically connect or disconnect both measurement leads. The center position is off, and the two ends do different things:

The 100 kΩ position: identifying high-source-impedance voltages

A voltmeter reading tells you a voltage is present. It does not tell you whether that voltage can do anything — whether it is a real supply, a reading sitting behind a large source resistance, or a few picofarads of coupling. The difference shows up the moment you load it, and the three switch positions give you three known loads without changing anything else in your setup:

The 1.1 MΩ is two 500 kΩ divider legs plus a ~100 kΩ sense resistor, and it is what the probes see whenever the bridge is in its resting state — which is almost always. The bridge switches off only for the brief instant of each open/closed test.

Read the same point in each position and watch what the number does:

• Barely moves → a supply rail. A stiff, low-impedance source: a real rail, a battery, an energized circuit.
• Sags significantly → a high-source-resistance voltage. Real, but behind a large resistance — a resistive divider, leakage, or a high-value pull-up. It reads full scale unloaded and cannot hold up under any load.
• Collapses quickly toward zero → a phantom voltage. Capacitive coupling from an adjacent conductor — see ghost voltage — not a source you can draw from at all.

If you want a number rather than an impression, one loaded reading is enough. With V_open measured in the center position and V_load measured across a known load R_load:

R_source = R_load × (V_open − V_load) / V_load

So a point reading 12 V in the center position and 6 V in the 100 kΩ position has a source impedance of 100 kΩ × (12−6)/6 = 100 kΩ. A point that reads 2 V open and 20 mV loaded is sitting behind roughly 10 MΩ — that is coupling, not a supply.

The math assumes the center-position reading is the true open-circuit voltage. Once the source impedance climbs into the megohms, your meter's own 10 MΩ is loading it too, and the calculated value reads low. For that range, treat the result as a lower bound.

What the verdicts mean at the bench

The reverse direction is trustworthy everywhere: a blue "Open" verdict means the probes genuinely see a high impedance — there is no low-resistance connection between them.

Sensitivity (most users can skip this)

Under the hood, sensitivity is a genuine tradeoff: more bridge resistance produces a stronger detection signal (better discrimination of high-resistance circuits) but slightly more ghost voltage on the host meter. Your unit is calibrated and set at the factory, and most users should simply leave it alone.

• The unit stores four sensitivity settings and uses one of them. The factory choice is tuned for everyday use with minimal ghost voltage.
• There is nothing to adjust on the outside of the unit — no switch, no dial. Changing the setting means connecting it to a computer over USB and sending one command, which takes effect immediately with no reboot or reprogramming.
• What each of the four settings means is itself reprogrammable, so one can be re-purposed for a specific application. Both are covered in the firmware manual.

What it can take, and what to keep in mind

• It sits beside your meter's inputs. Blinky Hawk connects in parallel across the same jacks your probes use — whatever your probes touch, it sees too. Its front end is built for that exposure: detection has been verified working from 0 V through ±1 kV, including −1 kV applied from a megohmmeter; beyond its sensing range the front end simply saturates behind its own series resistance and clamp protection — there is nothing fragile exposed to the probes.
• It is gentle on circuits. The injected test signal can never exceed the internal 1.25 V reference, and worst-case current into a dead short is about 6 µA, falling to nano-amps into high impedances — where sensitive electronics would actually care.
• Your meter's ratings still govern. Blinky Hawk does not change your meter's CAT rating, and it carries no independent safety certification of its own — observe the category and voltage limits of the meter and leads you use, exactly as you would without it.
• It is an indicator, not a lockout. Use it to catch unplugged-probe mistakes faster — but always verify de-energization per your normal safe work practice before touching a circuit. In particular remember the reactive-parts caveat in section 5.

Configuration over USB

Every behavioral setting — the four sensitivity thresholds, beep pitches and patterns, LED brightness and flash timing, detection timing, how aggressively the unit sleeps, battery calibration — is stored in on-board EEPROM and can be changed permanently over the USB-C port with simple text commands (or the companion desktop app), no reflashing required. The complete reference, including a serial-protocol table and step-by-step recipes, is the Blinky Hawk firmware manual.