It is said: “There are 10 types of people in this world, those who understand binary and those who don’t”. If you choose understanding side, then you might want to wear binary wristwatch.
Building such watch is fairly simple and easy, because you only need few components and even simpler code. Elias watch is based on PIC microcontroller which comes in SSOP-20 package. With few difficulties on soldering it to small PCB he had it running. Watch is powered from coin cell battery CR2032. With smart software solution combined with sleep modes this watch can last long. But the main point of wearing this watch to be identified as nerd. I’m not suggesting to replicate this one, but build your own version.
There is always a dilemma on how to build an indicator for your next project. There are many options like LCDs, LEDs, VFD. Sometimes one or another is enough, but eventually you want something eye catching and obvious that could be seen from distance. For instance for water meter a dial based display probably is better than LCD. IT can be seen from distance and is informative to tell how mutch water is in tank.
John simply built a LED ring display out of 16 single color LEDs. He needed to use shift register, but he thought that popular 74xx595 chip is very current limited. Total current draw shouldn’t exceed 50mA which is like 2 more powerful LEDs at a time. So he looked for more proper shift register and came op with better one – TLC59282 16-bit shift register which is capable of sinking 30mA on each pin. Neat feature of this chip is that it comes with current setting pin, meaning that you only need single resistor for setting current for all LEDs. This saves space on the board. He wrote a nice demo for PIC microcontroller which goes through several display effects. Once you’ve done playing you can use code snippets for displaying info on it like water level, RPM, speed or what ever you want.
There are several digital clocks with analog displays around. They are somewhat unique giving the feel of the retro. With proper enclosure such clock becomes great design element. Following project was inspired by Alan Parekh multimeter clock. Originally there were three analog multimeters used in voltage mode to display hours, minutes and seconds. In this project there are three analog voltmeters used with their faces printed to match time scale – one for hours, one for minutes and third for seconds.
The clock code runs on PIC16F628A but time is synchronized every 30 seconds to master clock. Analog displays are driven through transistors by generating PWM signals that are equivalent to DC voltage. This part is fairly easy to implement on microcontroller. The clock also has a Chime circuit based on ISD1730 that gives “tick tock” seconds sound.
Charging lead acid car is fairly simple. You need to take care of charging current which should be around 0.1C and charge up to 13.4V battery voltage. Having this in mind, it is easy to build charger out of few parts available. Pityukecske have shared his version of battery charger on instructable. He has chosen a PIC12F683 microcontroller which controls relay switching charging current to battery and also monitors battery voltage on one of its ADC inputs.
Current circuit doesn’t have much flexibility – charging current is basically driven directly from transformer and diode rectifier. It is visible on panel ammeter. So transformer is chosen to meet current requirements. Microcontroller monitors battery voltage. Since it is over 12V there is a resistor voltage divider used to scale voltage to microcontroller working limits. Once voltage reaches 13.4V, microcontroller shuts current by deactivating relay. Couple status LEDs indicate charging state. Simple solution that works in most cases.