by Ashish Kumar and Pushek Madaan @ edn.com:
In our modern era, digital logic has become the core of all the electronics circuits either in the form of an FPGA, microcontroller, microprocessor, or discreet logic. Digital systems use many components that must be interconnected to perform the required functions. The vital element for proper operation of such a digital system is a CLOCK signal that enables all these digital components to communicate and establish synchronization between them. Hence, we always need a source to generate this clock signal.
This source comes in the form of an oscillator. Although most of today’s microcontrollers have an integrated RC oscillator, the clock generated by such an internal RC oscillator is typically not good enough to support the precision required for communication with other modules in the system. Thus, an external oscillator is required that can provide a clock signal to the complete system and yet meet all the requirements for precision, signal integrity and stability.
Oscillators: How to generate a precise clock source - [Link]
This is a quick project for a timer. Recently I finished my UV light exposure box and thought that it will be convenient to have a build in timer to switch off the light after preset time. So I had a PIC16F628A lying around and after searching the web I found a Brazilian site (I think?) with tons of interesting projects with microcontrolers. This project is based on one of them.
The schematic uses the internal oscillator of the microcontroller which is enough accurate for my purposes, but as the pins 15 and 16 are left unoccupied, there can be connected external quartz resonator with better accuracy. As I said, this project is based on an existing project, but actually my schematic is quite different and the code was almost completely rewritten. My programming abilities are little rusty, but I think the final result is quite good.
Simple timer with PIC16F628A - [Link]
by Jeremy Cook @ makezine.com:
Most of us have probably seen clocks or numerical displays that flip sequential boards to display the next number in a sequence. If you wanted to take that a step further, you could make a replica of “Dottie,” which flips small dots as pixels. As the great video below says, it makes a “pleasant mechanical flipping sound all day.” It also tells the date, chimes every 15 minutes, and gives an animation show once an hour.
Dottie the Flip Dot Clock - [Link]
The ChronodeVFD is a personal project I’ve been working on for a couple of months. It’s a wristwatch built around the IVL2-7/5 VFD display tube. I originally purchased a few of these tubes to build a standard desk clock, but after playing around with them, I realized I could probably build a wristwatch too. The tube has a number of features which make it more suited than most Soviet-surplus VFDs for this purpose.
ChronodeVFD: Wearable Electronics VFD Wristwatch - [Link]
F*watch is a fully open electronic watch project featuring an integrated GPS receiver.
The development started at CERN as an after-work project to make a special present for a retiring colleague who likes hiking and timing.
The full design (electronics, mechanics and software) is available under free licenses and the design is exclusively made with free tools.
F*watch – a fully open electronic watch - [Link]
The MAX6369-74 series watchdog-only supervisors are available in tiny SOT23-8 packages and have selectable watchdog timeout periods (1.7ms to 104s), start-up delays (1.7ms to 104s) and output pulse widths (1.7ms and 170ms) depending on the part selected and the state of 3 pins (SEL0, SEL1, SEL2). These parts have several advantages over the historical “555” solutions. As well as the lower supply current (20µA max instead of 120µA max at 5V supply) the overall solution takes much less board area with the smaller package and the absence of large timing resistors and capacitors.
MAX6369 Series Watchdog Timers – [Link]
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]
A stable single transistor sine wave generator, that works with many values of input voltage. In PartSim you can easily change the value of the resistors and capacitors and observe the effect on the frequency of the oscillator. If you are manually calculating the frequencies, make things simpler by keeping the values of the resistors and capacitors equal (R5=R6=R7 and C1=C2=C3). You can see in the simulation that it takes a while to begin oscillating, and in ideal conditions it would need a signal to start oscillating, however in practice, noise begins the process without it.
2N2222 Phase Shift Oscillator - [Link]
Here’s Aon’s finished project the ytimer a visual feedback timer:
A countdown timer with super bright 7-segment displays that flash when the time is up, instead (or in addition to) an audible alarm.
The design is based on a PIC16F886 microcontroller which drives the displays using a TLC5916 LED driver and dual P-channel MOSFETs. A rotary encoder with a push button is used for input, in addition to two microswitches, one for power and one for toggling sound. The sound switch also toggles a green 0603 indicator LED.
The device is powered from two AAA batteries, which will hopefully deliver adequate battery life.
ytimer, visual feedback timer - [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]