Filed under: Programming
The first stage of programming the clock involves simply getting the minute’s digit, which is the digit furthest on the right, to count from 0 to 9. Using the flow chart in programming editor I programmed the picaxe. In this program I used let B0= 32, B0 gives a pin its name and 32 is the binary code that sets the minutes digit to 0. By adding an, if then command into the program I was able to loop the program around. Each time the program looped around and did not = 22 it – 1 from 32 which enabled the clock to count upwards. When it reached 22 the, if then command, would repeat the process. The first program shows the flow diagram, the second program is the flow diagram converted into basic using picaxe programming editor.
Filed under: Connecting Clock Components
After making the PCB’s the next stage was to connect the picaxe 18x project board to the main PCB using wire and solder. Then using ribbon cable I connected the main PCB to the display PCB. This was done using two connectors with IDC termination. Once the components were connected together and given power the display did not show anything.
In order to fault find it was necessary to use the oscilloscope. This is a type of electronic test equipment that allows signal voltage to be viewed as a two-dimensional graph (For more info on oscilloscope’s see link). To make the fault finding easier I disconnected the project board from the PCB and connected a protocircuit. It was easier to fault find using the wire switches connected to ground on the protocircuit. This enabled me to check each of the four inputs going into the 4511. Using a probe from the oscilloscope I was able to test the voltage going in and out of the 4511 BCD chip. A line going horizontally across the display registers how much voltage there is. Due to this closer inspection of the main PCB I was able to identify that one of the pins on the 4511 was not connected to ground. This was pin 5 the store input. Using a section of wire I connected pin 5 to ground, once this was connected the circuit and display were functional. I then wired the project board back to the main PCB and this was all functional. I can now start with the programming
Filed under: Making PCB's
Making the PCB’s
The PCB layouts from art worker are printed out onto assertate using a laser printer, the black image will end up as copper on the final PCB. The print should be of a mirror image of the circuit, as this will ensure the black areas of the artwork will be in contact to the PCB’s Photoresist during UV exposure.
The board is cut to size using a guillotine, this is then cleaned... The layout is then printed onto the board using the UV exposure unit. The exposure unit has a timer on it, it is important that this is set to the right time, in this case two minutes. Once complete, the printed boards are washed of using photoresist universal developer. This is done by placing the crystals into a tray and mixing them with warm water, the boards are then put into this and the solution washes away any particles. The layout of the PCB’s should become clearer and after one or two minutes they can then be washed of using water.The next process involves using Ferric Chloride, when using this safety gloves, classes and overalls must be worn. The PCB’s are place in the lid/mesh basket board holder of the developing tank. The Ferric chloride used in the tank must be kept warm at 45 degree C this is because it reduces the etch time from around 1 hour to 15 minutes. After several minutes, the copper will start to fall off, leaving the circuitry. Once complete the boards can then be washed, remembering to wear all the safety gear. Using a precision high speed drill and a 1mm bit the holes can then be drilled into the circuit.
Filed under: Designing PCB Using Curcuit Wizard
1. Circuit Diagram 2. Real world 3. Finished PCB
4. Art worker 5. PCB For Clock Display
Protocircuit and the photo and the diagrams show the progression of the design process of the PCB. This procedure had a number of stages these were:
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Using Circuit wizard I designed the layout of my PCB. I Used 2×4 pin single-in-line (SIL) so I could feed the eight out-puts from the picaxe project board onto the PCB. I also used 2×6 pin SIL for the ribbon cable to run from the PCB to the Display PCB.
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When the design was finished, I then converted the circuit diagram to a PCB layout. Circuit Wizard could only take this PCB layout to 94% efficiency. I then used circuit wizard tools to iron out any inefficiency in the design. During this process I had to actively delete, move and add components and lines. Extra time was spent on this part of the process. This was bacause in order to simplify the design of the display PCB, it would involve organising the 12 SIL pins. The 12 SIL pins were arranged in order from 1 to 12 with pin 1 connecting to pin 1 of the display this process was continued for all 12 pins.
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The final part of this stage was to print out from art worker the finished PCB layouts onto acetate.
Filed under: Circuit Diagram
This circuit diagram was used to simplify the layout of the circuit. I can now use this diagram and the protocircuit to design my final PCB layout before printing it in Art worker.
Filed under: clock development protocircuit
The next stage of the process involved connecting the picaxe project board to the protocircuit. The protocircuit is powered via the project board’s 4.5v battery pack. A positive and ground is wired to the protocircuit from the project board. The four switches that connect to ground will be replaced with out- put pins 4,5,6,7 from the project board. Out-put pins 0,1,2,3 from the project board are connected to pins 6, 8,9,12 of the four digit display. Now I know this circuit works I can start designing the layout of my PCB . It also allows me to start experimenting with programming.
Filed under: clock development protocircuit
The four inputs a, b, c and d on the 4511 connect to ground via four black cables (these can be seen in the previous entry) this gives the inputs a low reading. When these cables were removed the voltage pulls up through the 10k resister to the 4.5v and gives a high reading (1). Using these cables I was able to work out using a truth table how to count 0 to 9.
Filed under: clock development protocircuit
This protocircuit setup has moved on from the last protocircuit. On the previous circuit I was able to display three digits and count 0 to 9. The problem I had with this circuit was the numbers were not being displayed clearly. Other LED’s were lighting up causing the display to read unclear numbers. This is due to the electrons building up at the field effect transistor. This can be rectified by using 10k pull up resistors.
On this protocircuit I have used 10K pull up resistors on each of the inputs to the 4511 BCD. This enables the electrons that have not past through the field effect transistor to pass up through the 10K resistors. When the voltage to the inputs is connected to ground it give no pulse (0), when the connection to ground is disconnected it pulls up through the 10K resistors to the 4.5v giving the inputs on the 4511 a positive charge (1). This gives a much clearer display of the numbers.
Filed under: clock development protocircuit
In order to fault find, I have used a digital multimeter. Some of the digits on the display are not working. I used the multimeter to locate where there was a break in the protocircuit; this was stopping the voltage getting to one digit on the display. I also had some resistors with both legs on the same copper track on the protocircuit; this resulted in the resistor being bypassed and having no effect.
Filed under: clock development protocircuit
Initially the aim is to just get some numbers displayed on the four digit seven segment display. Using the circuit diagram from circuit wizard I was able to setup this protocircuit (See link for more info on protoboard). I also used the data-sheet for the four digit seven seg display. This enabled me to identify what each of the 12 pins on the display do. Using this data-sheet and the information I already had I was able to calculate what resistors were required between the seven pins from the 4511 and the seven pins on the display.
Calculations for Resistors.
IF=20ma Max Voltage 2.5 V/I = R 2.0/0.02= 1oo ohms resistor.
There is a 10% forgivness with this sum, so I selected 120ma resistors between the seven outputs of the 4511 and the seven pins of the display, the other five pins are connected to ground. These pins power the four digits and the dots between the numbers.
The 4511 is designed to be used with a common cathode display. The aim of this circuit is to count 0 to 9 on each of the four digits of the display. The diagram from circuit wizard demonstrates the possibility of using four switches as a means to input the 4511. An open switch represents 1 and a closed switch represents 0. Using circuit wizard as a means to experiment it allowed me to formulate a truth table. This can be used to identify the inputs needed for 4511 to display each number.
