I'm trying to design a wireless temperature sensor powered by one (or maybe two) rechargeable NiMH AA cell(s). The sensor should read and transmit the temperature every couple of seconds and remain in low power consumption mode the rest of the time.
I'd like the sensor to be built with the following components:
- ATtiny85-20PU or ATmega328P-PU as MCU (1.8-2.7 to 5.5V)
- TWS-DS-6 433.92MHz RF Transmitter (1.5 to 12V)
- The obsolete LM35DZ Precision Centigrade Temperature Sensor (4 to 30V)
To power these components with the batteries I chose, I suppose I'll need a boost converter that generates 4 to 5V out of 1.2 to 1.5V input (or 2.4 to 3V if I use two cells).
My problem is that I can't find the right boost converter that is simple and cheap enough for me to build, and that I can easily get parts for. For example, I've found these really cool resources online:
- Maxim's Switching Regulators for Battery-Powered Applications – a quick guide to choosing switching regulators for battery powered applications, with links to parametric searches on Maxim's site.
- Linear's App Note 30 – Switching Regulator Circuit Collection
From App Note 30 above, I could select a couple of circuits that I think could meet my requirements, such as:
- Figure 9. Boost Converter (1.5V to 5V)
- Figure 11. Single Cell Up Converter (1.5V to 5V)
The problems I have with those circuits is that I don't have easy access to some of the components, such as the LT1018, LM10 or the TRIAD SP-29 (I don't even know what that is), for example.
So, my question is what would be an appropriate boost voltage regulator circuit for my specs?
Best Answer
Why are you not going ahead with a standard DC/DC boost IC? Starting at $0.9, that should be fairly accessible to you. No reason to reinvent the wheel here. A quick search through digikey gives plenty of options with input ranges for this search going down to at least 1V input with 5V output.
Here's one of the datasheets on a cheap one. All you need to add is two caps and an inductor. You state that you're designing a wireless sensor module, not a DC/DC converter, so I assume my answer is valid for your requirements.
EDIT - Now that I know why you're designing a boost converter rather than buying:
I would go for a boost converter driven through a low voltage 555 if you can find one of those easily. If there's no low voltage 555 timers, you could also just use an oscillator to drive the boost converter. One oscillator that I've used previously is a ring oscillator with an RC addition for control knobs to drive a boost converter. I was able to achieve 18V out of 5V at ~80% efficiency. Another simple oscillator that could likely be usable is a basic astable multivibrator.
If you don't want to go with a standard oscillator based boost controller, you could try the the joule thief or something similar.
With any of these multi-chip or discrete component solutions, make sure you add in a 5V linear voltage regulator after it to ensure stable operation after the boost stage.