I want to build some small wireless temperature measurement boards, to sprinkle around the house. I'd like to power these from a single coin cell battery (CR2032).

For these I'd like to use the DS18B20 sensor. These sensor require a minimal voltage of 3v. A coin cell will however only provide 3v when it's full, and will drop to around 2.6v when 90% discharged.

From what I've read the DS18B20 will give some strange results when the supply voltage is below 3v. Also the precision can be off, when the supply voltage isn't regulated.

(The ATMega328p and NRF24L01, I plan to use, will work just fine at voltages down to 2v, so only the DS18B20 requires 3.3v.)

So I've come up with the following solutions:

  1. Use two coin cells, and a (low quiescent current) voltage regulator. (Disadvantage: takes more space, more batteries, slightly more expensive.)
  2. Use a boost regulator. (Disadvantage: even more expensive, and a lot more complex (for me at least).)
  3. Implement a voltage doubler to power the DS18B20 when needed (every 15 minutes). To regulate the voltage I'd add a 3.3v zener diode to the output. (dirt cheap to implement)

I tend to lean toward option 3, but my question is, could it even work?

Is there something to look out for?

Or is there an even better solution?

edit I was planning to use the Dickson doubler circuit.

voltage doubler

  • What type of voltage doubler are you considering? – Majenko Jan 16 '16 at 14:34
  • @Majenko A Dickson doubler. See the schematic in my edit above. – Gerben Jan 16 '16 at 15:35
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    A dickson is certainly a possible solution, and is commonly used in battery powered systems to get a higher voltage to run components that need it. Better though is to not need it in the first place since any voltage conversion will entail losses that will shorten your ideal battery life. – Majenko Jan 16 '16 at 15:57
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    If you are using a doubler you should use Schottky diodes to minimise voltage drop. Using a Zener diode without a limiting resistor would work in this circuit, but is likely to be very inefficient. A series regulator would be better. You could use a feedback circuit to vary the high phase of the clock as a simple switching regulator, and eliminate the Zener. – Milliways Jan 17 '16 at 4:39
  • @Milliways I'll have to calculate the correct capacitor value, and frequency, to match the current needed for the sensor. Any excess current will indeed be lost through the zener. – Gerben Jan 17 '16 at 13:00

You're missing out option 4, which is the option I would personally go for:

  • Use a different temperature sensor.

A quick parametric search on Microchip (my favourite, I'm a Microchip fanboy after all...) I find quite a nice one - the MCP9844.

Microchip Technology Inc.’s MCP9844 digital temperature sensor converts temperature from -40°C and +125°C to a digital word. This sensor meets JEDEC Specification JC42.4-TSE2004B1 mobile Platform Memory Module Thermal Sensor Component. It provides an accuracy of ±0.2°C/±1°C (typical/maximum) from +75°C to +95°C.

Operating Voltage Range (V): +1.7 to +3.6

However it is only available as a TDFN which makes prototyping difficult, although it is one of my two preferred footprints for real building - the other being variants of QFN.

I am sure you can search other makers for similarly specified chips that will do the job without the need for fancy boosters or doublers or the expense of multiple batteries etc.

One of the first steps of any design is the component identification. Often the chip or component that many people automatically reach for because it's the first one they used, or it's the one people most often talk about, may not be the right tool for the job. It pays to shop around a bit and look to see if there is something better that will fit the bill and save cost and time in the long run by ending up with a simpler system.

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  • That's an interesting alternative. I was indeed working backwards on a problem. I wanted to try soldering TDFN/QFN anyways. Thank you. I'll go and search some more alternatives, and see what's available from my regular webshops. – Gerben Jan 16 '16 at 15:59

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