For my dayjob, I work with people who have physical and mental disabilities. Some of these people are also analphabetic and that can sometimes cause problems for the work they have to do. One of the jobs they do is repackaging sweets. The problem is that repackaging sweets is always based on weight and that they are not able to read scales. So I decided to do something about that.
Since teaching them to read and write would cost me to much time, I decided to build a device that does that for them. My task was made a lot easier by the fact that we use industrial scales that have a serial output to connect it to a printer. It meant that I didn't have to open the scales themselves to hack a device into it. I could just add a serial device to it.
I came up with this device. It has 3 LEDs to display the weight. Green means that the weight is ok, red means that it is to low and yellow means that it is to heigh. A foreman can set the device up via the LCD and the rotary encoder.
It is also possible to set separate percentages that the weight can be above or below the required weight. I added that feature because sweets have a certain weight and it isn´t always possible to get the required weight exactly.
An extra feature is that the value off the desired weight and of both percentages are stored in the EEPROM of the device, so that it sets itself to the last used values on powerup.
Step 1: What do you need to build the circuit?
- A 16 x 2 LCD
- An Atmega8
- A 74LS04D
- 3 x 150Ohm resistors
- 6 x 10K resistors
- A 10K trim potentiometer
- 2 x 100nF capacitors
- A red LED
- A green LED
- A yellow LED
- A rotary encoder with a pushbutton function.
- A male 9-pin serial connector