What is worse than a battery powered multimeter?
A battery powered multimeter with an empty battery.
That’s why I have to upgrade this multimeter with a power socket, a step-down converter to support a wide input voltage range, and an isolated DC-DC converter to isolate the input voltage from the multimeter circuits.
I have the following things:
- 24VDC wires through the house for lighting and more.
- A 24VDC 10A power supply, can be adjusted with a potentiometer between 22V and 28V (more than the specified +-10%).
- Two 12V 7Ah lead batteries.
Now I want to combine them to get an uninterruptible light source.
At the house warming party we got a bedside lamp with watch from Somi. Since then it was sitting there beside the bed without beeing plugged in. You might wonder why… Because it contains an old fashioned light bulb.
Now it was time to change that. But the project became a little bigger than I wanted…
Today I fixed my battery light. I changed R15 to 39k, and for R14 I had used 33k since I didn’t have anything between 22k and 33k. The threshold voltage is now at most 7.3V so this rubbish wire can make a voltage drop of over 4V and it will still work. And just for testing I’ve put a 470uF cap instead of the 100nF for C5. I left this one inside, it makes a nice delay for the LDR just in case some stray light hits it. Here is the updated schema (more docs).
Now I’m happy with it. Except maybe I add a sleeping mode where it makes just enough light to see the walls, or adding a wire to the bathroom and putting a PIR sensor and an LED there, or …
Why use an Arduino? Why don’t you build your own PCB like I do?
This way you decide which AVR pin is used for what and how you layout your own PCB. And you can save a lot of money. On the other hand you have to invest some time to build it.
Today I finished version 2 of my battery light circuit:
I found the remaining inductor and soldered it onto the board. And I also added the connector, connected it to a LED and a power supply and switched on. And see! It works! Without any fiddling or whatever
And immediately I had to play around with it and combine it with a PIR sensor. The nice thing is that the circuits are almost fully compatible. The ouput of the HC-SR501 can be directly connected to the PWM input of the LED driver. And both run on the 12V power supply. Unfortunately the PIR will only work up to 20V so my planned 24V will be a bit too much for it.
Today I got my PCBs:
They look very nice Except that the mounting hole has not been drilled, very clever Have to find out what went wrong, but I guess I forgot to include the NPTH drill file. Who cares, maybe I’m going to cut away the last centimeter of the board anyway.
Here is one cut away and almost fully assembled:
I hope the PT survived the soldering torture. Hand soldering these is not so easy because they should have solder below them to make better thermal contact. I’ll find out if it works as soon as i found out where my inductors are hiding…