Power considerations

A project log for Self Ordering Hat Network

Hats that identify their physical layout and perform accordingly

Mike SzczysMike Szczys 08/16/2014 at 17:450 Comments

Powering the hat network is actually a bit of a challenge. Not because of the communication method; IR transceivers use very little power. But the display itself is quite power hungry.

Each pixel is capable of pulling 60 mA if driven white at full brightness. This is about 13.44 A if all 224 pixels are driven. This is unacceptable since the hats will need to use a portable power source. Preferably one that is hidden inside the hat itself.

But you can simply this. I figure the character with the most "on" pixels is the numeral "8". With the font that I'm using the number has 14 pixels illuminated. There is room for 5.3 characters on the display, or just over 74 "on" pixels. If I want to stay below 2.1 A, I can still drive the pixels at up to 28 mA. To give myself some headroom I'm going to drive them at a limited aggregate brightness of 66%. If done correctly a pixel should never draw more than about 13.3 mA (this is just a rough estimate based on the PWM value of an "on" pixel).