Opensprinkler pi unused zones voltage4/27/2023 ![]() ![]() Above all, it fits neatly into a mint tin.An Arduino pro mini programs the valve control.A single li-poly rechargeable battery drives the circuit and a 24v latch solenoid.Voila, here comes my minty water valve controller!īefore describing how to build it, let me highlight some features of it: So I thought that perhaps I can build a water valve controller myself and best of all, I can fit the circuits entirely in a mint tin. I was looking into some automatic watering option like this one, but it provides limited functionality and does not suit my need. Recently an idea came up: I had a new lawn installed in my backyard a couple of weeks ago, and I needed to start watering the lawn regularly everyday. For a long time I’ve been thinking of my own minty project: what can I build in a small mint tin? There is an entire webpage on Make that documents such projects. I’ve always been fascinated by minty projects - circuits that fit neatly into a mint tin. Comments and suggestions are welcome!ĭownload Arduino source code lcd1602a.pde. The schematic and source code for the example program are attached below. Right now it occupies 7 Arduino pins (1 of them has to support PWM), but this number can be reduced to 3 by using a shift register. In summary, this is an decent and inexpensive LCD, which works nicely with Arduino. Other microcontrollers might not be able to do so directly from their I/O pins. Arduino’s I/O pins can source or sink more than 20mA of current, which is sufficient to drive the backlight LED. Update: It’s ok to connect Arduino pin 10 directly with LED- or LED+ to supply the PWM signal without using a transistor. The video probably exemplified them, the actual LCD looks better than the video. Some ghosting artifacts are noticeable as the words move left and right. The program scrolls text left and right, meanwhile I use a timer interrupt to brighten and dim the backlight. ![]() Just to demonstrate it, I wrote a simple program based on the Scroll example provided in Arduino. With this, I can easily control the brightness of the backlight. This is very standard design, refer to the schematic below. The transistor serves as a current sink, and its base is connected to Arduino pin 10 to apply PWM control. In order to control the back LED brightness, I made use of a transistor (2N3904) and Arduino’s PWM (pulse width modulation) to adjust the effective voltage supplied to the LED. After some experiment, I found that the desirable voltage is about 0.65V, which can be supplied by the forward bias voltage of a standard diode, such as 1N4148. Normally the display contrast (V0) pin of the LCD is connected to a potentiometer in order to adjust the contrast voltage. Here is what I did: LCD RS, Enable, D4, D5, D5, D6 pins are connected to Arduino pin 12, 11, 8, 7, 6, 5 respectively. I made small changes to the pin assignment. Making it work with Arduino is straightforward by following the LiquidCrystal example. One downside is that the back LED is a bit noticeable (see the glow on the right edge of the display) also, the text will be almost completely invisible if the LED is turned off, so the LED has to remain on, consuming more power. The blue LED backlight looks quite pleasant. It’s HD44780 compatible, so it can work directly with the Arduino LiquidCrystal library. The model number is 1602a and the spec is easy to find online by searching the model number. Here are two images of the front and the back: The product was shipped from Hong Kong, so it took about 2 weeks to arrive. ![]() The total is only $3.49 including shipping. Then program it either via a RPi or laptop/tablet.Recently I was looking for a cheap 16×2 LCD, and I found several interesting models on eBay that come with great price. Also talk to a thermostat either a traditional 240V one or cleverer. That can hold a schedule, RTC and some relays. Presumably the best solution for heating control, like this lawn waterer, is to have a low power controller, such as an ATmega, and some custom electronics+ relays. This causes the poor relays to thrash, which in turn makes them sicker. So their repair is mostly replacing the relays (dead cheap).īecause of the logic states required to run a combie sick relays cause all sorts of problems cos a relay can contact, the board’s happy to switch the next device, and then earlier relay changes its mind so forcing the controller to backtrack. The 240V relays on the edges get trashed. What happens is that the extra-low voltage electronics lasts for ever. There’s a company that sells refurbed boards for a fraction of the price of a new one. Marginally OT, but the circuit board for a combie boiler wear out after a few years.
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