The Morse Thermometer - Part 3

Putting it all together
In part 1 and part 2 of this posts I investigated and designed the components for a solar-powered Morse thermometer. In part 3 everything gets connected.

In order to get the most out of the collected sunlight it is important to use as little power as possible. A red LED is a good choice here, because it only has a forward voltage of 1.7 Volts. So it will consume only about half the power of a white LED with a forward voltage of about 3.3 Volts.

Perhaps you remember that I had found out that even when the LED is not lit, the boost circuit from the solar lamp draws about 7mA. So it was important to switch it off during the time the thermometer is in stand-by.

Let's have a look at the original lamp circuit again.

The Morse Thermometer - Part 2

Reverse Engineering a Solar Lamp

Part 1 of this post is a write-up of my project for a thermometer with Morse code output. But I was not satisfied with the relatively high power consumption of the circuit, so I decided to use a solar cell to supply the circuit.

A cheap source of solar cells these days are solar garden lamps. You get them for very little money in garden centres and DIY shops. So I went and bought one. The general idea was that such a lamp would not only give me the solar cell, but also a water-tight enclosure, a rechargeable battery and a boost circuit so that all aspects of the power supply would be covered.

And the supply should be more that sufficient for my purposes, since in my thermometer, the LED would only switch on a fraction of the time. By setting the display cycle time carefully, it should be possible to supply the thermometer for 24h per day.

The Morse Thermometer - Part 1

Project Features

• Extremely simple hardware
• Low-Cost
• Uses the internal temperature sensor of the ATtiny25 

Introduction

I used to have one of those electronic thermometers with an outdoor sensor. That sensor transmits its readings through an RF link. Except that it didn't really work. Every now and then I had to reset the thermometer so that it would re-connect to the sensor. This annoyed me and I thought maybe I could make something that actually works.

Well, that was my excuse for this project...