In this new project I am again using PIC16F628A microcontroller. The goal is simple digital clock with 7-segment LED display and the clock will have no additional functionality – no alarm, no seconds digits, no date. The latter can be added in the software though. For the RTC chip I chose DS1307. For the LED display I used Kingbright CC56-21SRWA.
The input is at 50Hz and the output is at 60Hz. So for every 5 input cycles, we want to generate 6 output cycles. We will be synthesizing a sine wave in software, and there’s no reason not to go with a conventional lookup table of 256 bytes. The PWM will be averaged out by the coils in the motor. It may even be possible to drive it with a square wave, but there is a self-starting mechanism I don’t want to interfere with. A synchronous single-phase motor normally will spin in either direction, and if you want it to spin only one way (as is the case with a clock) extra components are needed. It could be a mechanical pawl that stops it starting in the wrong direction, but the rotor spins very freely in either direction when the clock is powered off. More likely, there is a capacitor and/or additional coils which provide the shove in the right direction.
Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:
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This is a battery-powered EV charger that allows destination charging where L2 charging is not ordinarily available. This can be used as a range extender for electric vehicles with smaller batteries. This system has a ~7kWh battery which should charge my Cadillac ELR to more than 60%. This has been a fun project with plenty of lessons learned.
Ryan Flowers writes, “A fun project for every QRP enthusiast is an L-match tuner. We’ve built a couple here at MiscDotGeek and our latest build inspired Billy Dunn (AF5HD) to build a similar tuner. We have to say, this one turned out better than ours did!”
App note from Maxim Integrated discussing strain gauge and accompanying circuit are used in today’s weight measurement applications. Link here (PDF)
Current laws and regulations require honesty, tolerance, and accuracy in weigh scales. The most commonly used weight-measurement element is the strain gauge. This application note explains how strain gauges are useful in multiple applications that must measure stress and pressure and their effects. The electronics of honest weigh scales are varied, and can provide the resolution and accuracy that each application demands.