It's been awhile since my previous post about designing a name badge to wear at Maker Faires. I didn't finish my "PdP7" twitter name badge in time for Maker Faire: Bay Area, but I was able to wear it to Ann Arbor Mini Maker Faire:
Several folks commented they dug it including the cook in the toasted cheese grill truck (which was delicious). One guy even told me about how he used to program a PDP-8 minicomputer back in the day!
While hard to see in daylight, the LED segments are quite visible indoors and, thankfully, most of the faire was inside. The common anode of each 7-segment display is driven directly from a separate PWM pin on the 3.3V Arduino Pro Mini. Here's a quick diagram made in Fritzing:
The 7-segment datasheet lists the min Vf as 3.2V and max Vf as 3.4V. Each display's LEDs are not getting as much voltage as recommenced after the drop from the current limiting resistor connected to the common anode. I could have powered the displays via the 3.7V LiPo battery voltage and used the Arduino pins to control transistors. However, I decided against finding space for 4 transistors and went with the direct approach (after measuring the current consumption is below the Arduino per pin max).
Here's the connections on the backside:
I found a nice pouch at Staples which it all fit in. I also used a name badge sticker to diffuse the 7-segment displays since they were uncomfortable to look at when at max brightness indoors:
Here's the simple pattern I programmed. The speed can be adjusted with the potentiometer:
The final version of the Arduino sketch is in my pdp7badge repo on GitHub.
I had prototyped with a 850mAh LiPo battery, but I ended up using a more compact 400mAh LiPo in Ann Arbor. I was very pleased that it ran for more than 12 hours before running dead sometime overnight:
Next stop for the "PdP7" badge: Maker Faire: Kansas City this weekend!