LED card

I’ve been thinking about making an SMD LED card for a while and as my friends Ky and Jenny were departing from Falmouth for Brighton, I though it would make for a good present. Here’s a video of the finished thing.

I started by drawing out the circuit schematic in Eagle. I based it around the videos I’d seen for making a LED knightrider circuit using a 4017 decade counter and a 555 timer. Here’s a link to the page I used.

A basic explanation of how it works is that the 555 timer is set up as an astable pulse generator, so the ouput of the 555 oscillates between 0V and 5V(low and high). This is routed to the decade counter. The decade counter has 10 outputs, 9 of which stay low and 1 is high. Each time the 4017 input goes from low to high, the output pin that is on moves to the next pin. This basically cycles through the ouputs, which are in turn connected to groups of LEDs.

Each ouput pin of the 4017 drives between 1 and 5 LEDs. This requires between 20 and 100mA of current. The 4017 is only rated to give 20mA so I had to put a MOSFET inline with each ouput. This acts as a switch that only uses a small amount of current to turn on or off but connects the LED groups directly to the main power lines.

To adjust the frequency of the 555 output, which changes how fast the 4017 cycles through the LEDs, I added in a very small potentiometer and also a surface mount slide switch.

Below is a schematic and parts list which includes Farnell order codes.

Part Device Value Farnell order number
BAT1 AA battery holder 908733
BAT2 AA battery holder 908733
C1 0805 capacitor 1uF 1828853
C2 0805 capacitor 10nF 1414662
C3 0805 capacitor 10uF 1833812RL
IC1 CMOS decade counter CD74HC4017 1739754
IC2 SMD timer NE555D 1737167
LED1 0603 LED pink 1685073
LED2 0603 LED orange 1710526
LED3 0603 LED orange 1710526
LED4 0603 LED orange 1710526
LED5 0603 LED green 1226372
LED6 0603 LED green 1226372
LED7 0603 LED green 1226372
LED8 0603 LED green 1226372
LED9 0603 LED white 1716769
LED10 0603 LED white 1716769
LED12 0603 LED white 1716769
LED13 0603 LED white 1716769
LED14 0603 LED white 1716769
LED15 0603 LED blue 1686063
LED17 0603 LED blue 1686063
LED18 0603 LED blue 1686063
LED19 0603 LED blue 1686063
LED20 0603 LED blue 1686063
LED22 0603 LED blue 1686063
LED23 0603 LED green 1226372
LED24 0603 LED green 1226372
LED25 0603 LED green 1226372
LED27 0603 LED yellow 1226417
LED28 0603 LED yellow 1226417
LED29 0603 LED yellow 1226417
LED30 0603 LED yellow 1226417
LED33 0603 LED white 1716769
LED34 0603 LED white 1716769
LED35 0603 LED white 1716769
LED38 0603 LED white 1716769
LED39 0603 LED white 1716769
LED40 0603 LED pink 1685073
LED44 0603 LED pink 1685073
LED45 0603 LED pink 1685073
LED49 0603 LED pink 1685073
LED50 0603 LED pink 1685073
Q1 SMD transistor MOSFET-NCHANNELSMD 1758065
Q2 SMD transistor MOSFET-NCHANNELSMD 1758065
Q3 SMD transistor MOSFET-NCHANNELSMD 1758065
Q4 SMD transistor MOSFET-NCHANNELSMD 1758065
Q5 SMD transistor MOSFET-NCHANNELSMD 1758065
Q6 SMD transistor MOSFET-NCHANNELSMD 1758065
Q7 SMD transistor MOSFET-NCHANNELSMD 1758065
Q8 SMD transistor MOSFET-NCHANNELSMD 1758065
Q9 SMD transistor MOSFET-NCHANNELSMD 1758065
Q10 SMD transistor MOSFET-NCHANNELSMD 1758065
R1 0805 resistor 82k 1100327
R3 0805 resistor 120R 1738947
R4 0805 resistor 39R 9334467
R5 0805 resistor 30R 9334297
R6 0805 resistor 24R 9334181
R7 0805 resistor 24R 9334181
R8 0805 resistor 120R 1738947
R9 0805 resistor 39R 9334467
R10 0805 resistor 30R 9334297
R11 0805 resistor 24R 9334181
R12 0805 resistor 24R 9334181
U$1 0805 resistor 50k 9608257


Once I had the schematic sorted, I went about laying it out on the board in Eagle. After spending a while laying it all out I printed the design to a PDF using CutePDF to ouput it as a vector image to do some graphic editing.

I could then open it up into Illustrator and play around with the lines. I added in some text and made a few of the signal lines curved.

At this stage it could be used as an etch resist pattern for use with the toner transfer method or similar. I use a little Roland MDX15 CNC machine. It uses a print driver that I have to create the cutting lines. I did this by using the offset path function.

Here’s some images of cutting it out

I then had to do some of the most fiddly surface mount soldering I have done, but it turned out OK in the end.