So before I get ahead of myself, I decided I need to actually finish my projects. I can't forget about the LED flash and the PortaLED (and the timelapse slider which I really should finish sometime instead of doing other things).
To finish off the PortaLED, I plan to build a full enclosure out of PCBs and redesign it to actually be portable like a keychain light.
The biggest electrical changes that need to be made are:
- Smaller inductor (use the 1.6 MHz version of the LM3410)
- Smaller diode
- Proper Power OR
- Buttons and switches on the board
When I was browsing Instructables, I came across this mini LED cube pendant:
http://www.instructables.com/id/LED-Cube-Pendant/. I found the compact construction and use of PCBs for the entire frame really well done, and in the circuit the author described a simple power OR circuit that would fit my needs. The use of a P MOSFET in the reverse direction and a diode would properly OR the battery and USB/ISP power so that the battery is not back charged by the ISP header and that when it is plugged in the battery is not charging and discharging at the same time. I also came across the MAX40200 ideal diode in my search for a solution and was tempted to use it, but found out that there are ICs with the P-FET and diode all in one package (from the site I saw before!: http://cameroncharles.blogspot.com/2012/01/petzl-zoom-led-conversion-final-chapter.html; he had the same OR and I didn't even realize!). I'll also be using the same smaller diodes the blogger used.
The OR is really quite clever; the internal body diode conducts when only the battery is connected and causes the VGS to become quite negative, turning on the FET and allowing the battery to connect with little forward voltage drop. When the USB is connected, the gate is pulled high and the FET stops conducting. The body diode will also not allow current to flow backwards into the battery. The FET's arrangement is just like when it is used for reverse polarity protection.
And now I realize my circuit is effectively a clone of the one above. Which is fine with me.
5.8.18
My PCBs should have arrived at my home today (still at school) and I just ordered enough parts to make three complete lights. I ordered my PCBs from PCBWay, and holy they are fast. I placed the order on the 3rd, and they are delivered in just 5 days. Crazy. Ten boards for $5. (shipping is $20, but that really isn't that bad.) I will be using them again for sure for any boards I need in higher quantities and bigger than 3 sq in. Hopefully there are no errors in the layout (it's almost the same from the last revision).
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| 11 (!) Red PCBs. |
Time to begin planning out the larger lamp I have in mind.
5.12.18
Now I'm back home, I was able to solder up a board. There are still issues with the design, and I'm not sure what is causing it. Just like the first version, after programming the microcontroller the light is unable to sustain and brightness except the lowest one. The other modes just blink. Also, the LiPo I was using was somehow depleted to far below safe levels (maybe a short?). When I directly connected the DIM pin of the LED driver to VCC, the LEDs did turn on to full brightness, so I know the LED driver works. However, with the small 4.7 uH inductor rated for 1.2A, the inductor started to smoke. Changing it out for the 16 uH inductor from the previous version fixed that issue (although it is much bigger).
I can't figure out what is going on with the microcontroller and why it won't output anything on the PWM pin. I feel that there might be a brown out when the system turns on. I also noted that when the system is running part of the rail drops to ~2V (not sure why). How did this circuit work before?
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