CVS Oral Thermometer Dissection

Posted on Feb 7, 2014

This very simple high-level design demonstrates the product`s structure. Its integrated circuit responds to button presses and senses temperature via the probe, displaying the temperature on the LCD and sounding the buzzer when finished. This more detailed diagram shows that the temperature probe is part of a temperature measurement circuit. There

CVS Oral Thermometer Dissection
Click here to download the full size of the above Circuit.

is also what appears to be a normalizing referenc circuit. Finally, this diagram incorporates the unit-selection jumper only visible on the PCB. This schematic illustrates the relative simplicity of this thermometer circuit; most of the work is done inside the IC. The themal device works with R3, R4, and C1 to make a temperature measurement circuit, with the variable thermal device affecting the circuit`s time constant. The LCD is driven via a 16-bit bus, and the buzzer has a two-wire interface for sending pulses. The operation of R2, C2, and C3 is unapparent, but the waveforms on R1 seem to suggest that it provides a reference circuit for normalizing temperature measurements. The jumpers (disconnected pads) A and B can be used to switch the thermometer into Celsius.

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