Meter clock: keeping “current” time. Read more about the clock:
I’ve seen a few meter clocks in my travels of the web, and I love the idea. A few days ago, I decided that I must have one of my own. Such began the “How to do it” pondering cycle. I had seen builds where the face plate of the meter is replaced. This works, but I wanted to try and find a way to do it without modifying the meter, if possible. After some more ponderation, I came up with what I think is a serviceable idea.
I came across this style of milliamp meter on Amazon. They’re not quite 0-60 mA, but the 0-100 mA (a 0-20mA meter for the hours) is close enough. And they were cheap. So yay.
Part of my requirements were that the clock run off of an Arduino Pro Mini I had lying around, and with minimal additional parts. In order to drive the meters with some degree of precision, I would use the PWM pins to vary the effective voltage across a resistor in series with the meter. This would, by the grace of Ohm’s Law, induce a current that, based on the PWM duty cycle, would be scaled in such a way as to move the needle on the meter to the corresponding hour, minute, or second.
One minor issue came up in the form of the max current the GPIO pins on the ATMega328 chip can source/sink. The pins can source/sink a maximum of 40mA, a bit far from the 60mA needed for the minutes and seconds meters. Enter the transistor.
Using a simple NPN transistor switch circuit, I was able to provide the current for the minute and second meters from the 5V supply. The PWM signals switch the respective transistors on and off, effectively varying the voltage across the resistors in series with the meters.
The resistor between 5V and the meter is actually 2 1/4 watt 100 Ohm resistors in parallel for an effective resistance of 50 Ohms. The two in parallel was necessary as 5V x 0.06A = 0.3W (more than 0.25 that a single 1/4W resistor can handle safely).
Meter clock: keeping “current” time - [Link]
Brett’s new masterclock is Arduino-controlled and keeps very accurate time by periodically synchronizing with the DCF77 “Atomic” Clock in Mainflingen near Frankfurt, Germany. The DCF77 library for Arduino is used to decode the time signal broadcasted from the atomic clock. The time is displayed as hours, minutes, and seconds on six 1″ seven segment LEDs. A 4×20 I2C LCD display is also used in the project to display additional info such as display brightness, sync information, signal quality, auto tune’d frequency, auto tuned quartz accuracy, etc. Both the displays are auto-dimmed based on the surrounding light intensity using an LDR sensor and pulse width modulation technique. His clock also includes a bluetooth link for updating the Arduino firmware from a PC without an USB cable.
Very accurate master clock synchronized to the DCF77 time signal - [Link]
Want to build your own world clock? Check out Wouter’s DIY word clock instructables:
…I have found one DIY project that really stands out: Elektronika.ba’s wordclock, proving that it is possible to build your own wordclock that is as pretty as the original. Also, here is a video of the manufacturing process of the original: QLOCKTWO manufacturing
I have decided to build my own version, taking some queues from the sources in the above and making some changes (and adding some mistakes) of my own. Along the way, I have tried to take many pictures and I have written a build report in the form of this Instructable.
DIY word clock - [Link]
Johannes’ Numitron GeekWatch features Numitron tubes housed in a hideous 3D printed case:
Numitron tubes are cut-down version of Nixie tubes, but instead of having a wire-mesh anode with a cold-cathode display, uses a seven-segmented indicator commonly found on digital meters and clocks.
Old School Tube Watch - [Link]
This Instructable describes building of a fun and very simple LED clock using Arduino that displays the time to the nearest half hour using LEDs.
Arduino LED clock - [Link]
Elia wrote an article detailing his binary wrist watch project:
I have just finished my binary wrist watch project (well, the new revision anyway). I was surprised at how small I was able to make it compared to last time.
I chose to go with the “super-yellow” color LEDs as they fit the purple OSHpark PCB very nicely. The biggest challenge was actually making a good looking wrist band for the watch. I originally intended to use a design like this but it turned out that due to lack of enough para cord I had left, I went with a simpler design that I had done once before.
DIY binary wrist watch - [Link]
Here’s a voltmeter clock project based on a multimeter clock design by Alan Parekh:
I have used three voltmeters and mounted them on a wooden plinth with a clear Perspex cover to give the clock an industrial look.
I have modified Alan’s code to run on PICBasic Pro version 3. I have also added the following.
Switched display On and Off (keeping battery backup as per Alan’s design) but also allows me to turn meters Off in full power mode.
Synchronization to my Master Clock every 30 seconds
Synchronized LED & Re-Synch LED
Synchronization On & Off
Transistor meter drivers
Separate hourly Chime Circuit
Pulsed “tick tock” seconds sound.
Voltmeter clock project - [Link]
Kerry Wong writes:
DS3232 is an extremely accurate RTC with a guaranteed accuracy of 2.5 ppm (0 °C to 40 °C), which translates into an error of just 80 seconds over the course of a year under the worst case scenario. I had done a few projects using this chip before (you can read about them here).
While by default DS3232 is already very accurate, we can push its accuracy even higher by adjusting its aging offset register (8bit). This adjustment works by adding or subtracting the corresponding capacitance to or from the oscillator capacitor array. The adjustable range is represented as 2′s complement (-128 to 127) and each LSB change corresponds to roughly 0.1 ppm of change in frequency. So the overall adjustment range can be achieved programmatically is roughly ±13 ppm.
DS3232 clock frequency calibration - [Link]
by Shawon Shahryiar @ embedded-lab.com:
Okay firstly the reason I wrote about the clock system instead of I/O ports or something else in this second post of the XMega series is simply because of the fact that without understanding clock configurations you won’t get what you want from your chip. Since XMega’s clock system is software-level configurable and complex at first, it makes itself the first priority module before anything else.
XMega Clock System - [Link]
Once all the components and headers were soldered in, I attached my Arduino and configured it as an ISP. I then burned the bootloader for an Arduino Uno.
I then connected my FTDI programmer and uploaded the blink sketch.Success!
Wow, that LED is super bright! It’s actually blinding and kind of hard to look at. With that, I swapped out the resistor for a 1K one in order to bring the brightness down.
Knowing that the Atmega worked, it was time to solder in the rest of the components, except for the display. Again, I don’t want to come this far and then waste a $15 LCD.
LCD clock version 2 - [Link]