The Nokia 3120 Keypad SMS Sender has been updated to v1.1 to use the ATtiny261 and another ULN darlington array. View the project page.
v1.1 (29 January 2012) – Download
- Uses ATtiny261 to remove the extra transistor / mosfet circuit
- Uses a ULN2003A instead of 4 transistors
- Use a spare output on a ULN2003A to turn the phone on when we want to send an SMS
therefore saving the battery until we need it
- Use the watchdog timer instead of delay_ms
It’s been a while since I etched any boards but I got around to etching the Low Voltage Battery Monitor PCB yesterday.
I did have a slight issue with the 3V battery holder, it was supposed to be mounted on the top but the battery holder that I was using in Eagle was smaller than the real thing so I just mounted it on the bottom. Version 1.1 fixes this issue. Other than that it works well and I can now say is the largest PCB I’ve made.
Today we’ll be making a simple circuit to detect whether a blackout has occurred and when it has we can be alerted, it should be non-contact so we don’t need to plug it into a power point.
From my previous projects I’ve noticed that the ADC in MCUs can be quite sensitive, if you leave the ADC ungrounded and do a reading it fluctuates. When you connect a floating wire and then touch the wire or move it around you can see even more fluctuations.
We can use this to our advantage, by placing a high value resistor like 1 Megaohm to ground then when some interference is detected it will fluctuate from reading 0 (ground). After some testing, it’s best to read the ADC multiple times in a short amount of time rather than just reading once and relying on that reading. We’ll be using it to detect AC interference by placing it near power points or power cords.