This is the second in a series of posts about designing a mains frequency monitor using the Microchip PIC 16F1619 microcontroller. In this post we will take a look at the first revision of the board that I designed for the project and some of the features that it adds.
Be sure to read Part 1 of the project write-up if you haven’t done so already.
The PIC16F1938 is a versatile 28-pin MCU belonging to Microchip’s extreme low power microcontroller family featuring nanoWatt XLP technology, 28KB of programming memory, 1KB of RAM, 11 ADC channels, and tons of other peripherals. A while ago, I designed a development board for this MCU and I thought it would be worth sharing this design here. The development board features an onboard USB-UART bridge to support the ds30 Loader for easy programming of the PIC MCU. All I/O pins are accessible through 2×5 headers.
I credit the maker movement with bringing electronics back from the crusty old and lonely electronics hobby back into the main stream. The Arduino is the micro of choice for this army of makers and I conceded it made sense… you install the IDE, plugged in your board into the USB port and a couple clicks later and you have an LED blinking.. the most exciting blinking LED you’d ever seen in most cases. I stuck with the PIC micros because I didn’t see any need to put back on the training wheels.
I got invited to a conference call earlier this week as they rolled out MPLAB Express. I almost passed the email up as spam, I’m glad I didn’t… a quick half hour later and I was in shock. Microchip is now relevant in the hobbyist realm.. They just leapfrogged over Arduino in usability for the beginner. They just released Microchip MPLAB Express a new, free, online cloud-IDE. Write your code (or pick a sample), press the compile button and the .hex file downloads.. DRAG AND DROP the .hex file on to the dev board. … the dev board looks like a plain flash drive… just drag and drop and the code is automatically programmed to the device… DRAG AND DROP.. brilliant.
This is an automatic “monitor brightness controller” based on environmental light conditions. This system use USB port base sensor unit to measure the light level and control monitor brightness accordingly. We design this system to reduce the eye stress by matching the monitor brightness with environmental lighting.
My Sony integrated amp with copper chassis and huge toroidal transformers was a tour de force in my audio setup before the power mains took an indirect lightning hit. Because the microcontroller was fried, I couldn’t even get the unit to power up.
Without access to spare parts — including a new microcontroller assembly — I was at the mercy of factory certified technicians. And — because the unit was just out of warranty — I was going to be out $100 plus shipping in order to get an estimate on the repair.
I recently purchased a used 10A Carroll & Meynell Variac from eBay for use in the lab, however the variac often caused the 32A B-curve MCB in the consumer unit to trip due to the high inrush current of the variac core. To prevent this from happening and to add a few additional features I created the soft start circuit outlined on this page.
The idea of the soft start circuit is to limit the inrush current whilst the variac core is first magnetising. There are many ways to achieve this and most involve adding some form of resistive element in series with the transformer to prevent the transformer appearing as a very low impedance to the mains AC supply.
The method used in this project was to use a high power resistor in series with the transformer to limit the current. Once the current has settled, the resistor is shorted out by a relay to then allow the full load current of the variac to be drawn from the mains.