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Instant-Read Thermometer: Digital, with a Stainless Probe That Pivots on the Case (Cook, US 5,018,875, 1991)
Penny

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Penny

3. November 2026DK
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Instant-Read Thermometer: Digital, with a Stainless Probe That Pivots on the Case (Cook, US 5,018,875, 1991)

A pocket digital thermometer. A thin stainless steel probe with a thermistor in its tip pivots on a small, flat-sided case, so you can push the probe into food and turn the display to face you. A button cell runs a chip and a liquid crystal display, and a push button updates the reading at once. The angled case will not roll off a table. Result: a thin-probe digital thermometer for food and air. Source: T. A. Cook (PSG Industries), US 5,018,875 (1991). Unknown: the circuit, the range, the case size. Picture: the patent drawing.
Intermediate
Unknown

Instructions

1

Make the probe

Cut a type 304 stainless steel tube about 0.166 in (4.0 mm) across and 5 in (120 mm) long, and close one end. Set a thermistor inside the closed tip and run its two wires up the tube. Aluminium or titanium would also serve.

Materials for this step:

Stainless Steel TubeStainless Steel Tube1 probe
NTC Thermistor KitNTC Thermistor Kit1 thermistor
Copper WireCopper Wire1 interconnecting wires

Tools needed:

HacksawHacksaw
Soldering IronSoldering Iron
2

Mould the pivot boss and case

Mould from ABS a cylindrical pivot boss with a recess for the probe's open end and a channel right through it for the wires. Mould the case in an upper and a lower half that snap together, wider at the display end and tapering to the probe end so it cannot roll, with two projecting supports at the probe end, each with a pivot hole. Not given: the sizes.

Materials for this step:

ABS PelletsABS Pellets1 boss and case

Tools needed:

Injection Moulding MachineInjection Moulding Machine
Unknown DimensionsUnknown Dimensions
3

Fit the electronics and assemble

In the case, fit an integrated circuit that turns the thermistor's resistance into a reading on a liquid crystal display at the wide end, with a push button beside it that updates the reading at once. Add a compartment for a 1.5 V button cell (Eveready E675, IEC R07) under a cover that locks with a quarter turn. Push the probe into the boss, lead the wires through the channel to the circuit, and clamp the boss ends in the pivot holes as the halves snap together; friction holds whatever angle you set. In use, push the probe in, turn the display to face you and press the button. Not given: the circuit (the patent points to US 4,536,851).

Materials for this step:

Printed Circuit BoardPrinted Circuit Board1 piece
Integrated CircuitIntegrated Circuit1 piece
Segment LCD PanelSegment LCD Panel1 piece
Push ButtonPush Button1 piece
1.5 V Button Cell1.5 V Button Cell1 piece
Solder WireSolder Wire1 as needed

Tools needed:

Soldering IronSoldering Iron

Materials

10

Tools Required

4

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