This schematic is ment to digitally display the output of an electronic Swissflow SF800 flow sensor. This sensor puts out an open collector square wave signal (like a fan RPM monitoring signal) between 50Hz (=0.5 liter/minute) and 2000Hz (=20 liter/minute).
By dividing the measured frequency by 10 and putting the decimal point at the right place you get directly a display in liter/minute. I don’t use the first digit output (output D) from the 74C925 to obtain a display of 10 to 9990Hz or xx.x liter/minute.
3-Digit Frequency Meter: [Link]
Mobile infrared electronic transmitter
I wanted to build an etching tank since i first saw one in an article on Make Blog. It was fun to make it and it will sure speed-up my PCB making process. The main thing that i wanted to achieve with my etching tank was to keep it thin so it holds up smaller amounts of etchant, it’s better this way because i need to store and work with smaller quantities. My finished tank holds 1,5 L of liquid when full.
In the article on Make the author made he’s from acrylic magazine holders. I chose to make mine from plexiglas. I got this 1500×1000x3 sheet for about $15 and now i got enough left to make cases for other projects. When working with plexiglas there are several methods of cutting it which include sawing it, cutting it with a hot wire or cutting it glass style. I used the method glass style which means you make repeated scratches on the same path using a sharp cutter.
Depending on the thickness of your plexiglas you have to make more or less deeper scratches. You’ve reached the desired scratch depth when you try to bend the plexiglas and it just snaps along the line. I would of shown you pictures from the making process but unfortunately i accidentally erased them 
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For gluing i used a PVC adhesive from Bison, it’s supposed to be used when gluing PVC pipes so i figured it should work on plexiglas too. The nice thing about it is that is leaves a nice transparent finish. After gluing i left it to harden for 24 hours.
Before assembling the etching tank make sure you’ve drilled holes for the heater and the hose.
On my DIY Etching Tank i also used a heater(an old aquarium heater that i used when i was into aquariums) to heat the etchant because heating it makes the process faster. Besides the heater i also added an aquarium pump that will agitate the liquid thus making the process even faster.
The parts used in the making are:
- 1500×1000x3 sheet of plexiglas $15
- PVC Glue $4
- aquarium heater $10
- aquarium air pump $10
- aquarium hose and disperser stone $2
Total: $41 . So with a little over 40 $ you can make your own etching tank
Here are some pictures with the tank being tested with watter:
You all know what a cable tracer is, and if you don’t let me give you a quick info: a cable tracer is a tool that helps you detect cables hidden behind walls or underground. It’s a goo idea to avoid damaging cables so this kind of devices are widely used in the industry.
The system works by injecting a 125-kHz signal into an underground cable. A pick-up coil receives a sample of the field. The field’s strength indicates the presence and direction of a cable. Simple ! now all you have to do is build it.
PIC Based Cable Tracer: [Download Project] - [View Project PDF] - [Via]
This project scans a 180 degree area from about 6 to 21 inches (15cm to 53cm) away and displays the information on a color LCD. To do this is uses. An infrared distance sensor from Sharp and an ultrasonic sensor from MaxBotix. This project is a short range, infrared and ultrasonic scanner that uses a standard hobby servo to move the sensors and a color LCD screen to display the information from the sensors. The information displayed on the LCD is an overhead view of the scanning area, with increments of distance from the sensors.
ATMEGA32 Based Infrared and Ultrasonic Scanner: [Link] - [via]
The Sprinkler controller was designed to act as a interface and controller for managing sprinkler system valves (also called zones). Those that exist either use what I consider to be unreliable protocols (X10), have a very limited number of valves (like 6 or 8), aren’t opto-isolated (i.e. just relays, pratically guaranteed to send huge transients into your automation system) or are just expensive (like $250 for 8 zones).
Currently i don’t have a lawn so I’m not too interested in this kind of projects, but i thought you might be.
27 Zone Sprinkler Controller With Pump Control: [Link]
