Some History
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This was my first successful test to combine a boost circuit with an ATtiny13A.
I hooked up a stock Nanjg110 to an ATtiny13A and a capacitor, both remainder of a Nanjg AK47. I added an OffTimeCap between Pin-2 and GND. And I used an IRLML0030TRPbF as FET. I placed the FET on the pads for a 7135, cut the traces and rewired (better: re-blobbed) for the PWM signal from Pin-6.
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I flashed a it with an offtime firmware with 4 modes.
And there was light.
At 18kHz PWM values of 2 – 10 – 40 – 255 resulted in 12mA – 102mA – 198mA – 404mA with a single full and resting Eneloop.
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With 2xAA the boost controller died (blew a tiny fan of smoke) at one of the first mode changes. It’s surely the controller that died, I swapped this single component from a new 110 and everything was working again (with 1AA).
That’s when I took a closer look at the Fasttech boost driver (who has a controller for modes) and the two resistors there seemed to serve as protection.
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In the meantime I found a replacement diode for the large SS14/SS24. As I looked for 2A diodes I stumbled upon the BAT60A.
Even rated 3A, only 370mV forward voltage, and SOD-323 package. It’s the teeny-tiny component on the right, where the cathode line uses up almost half the component.
I hooked it up in replacement and drained 5× 1AA and 6× 2AA (Eneloops) on this driver, while monitoring input and output current. Works perfectly fine. Even increased output current in 1AA config and efficiency in 2AA config (needs a lower input current to reach the 920 mA).
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Then I reworked the FastTech driver (comes in blue now instead of green).
MCU changed to Attiny13a (which was pre-programmed)
Some MCU-traces cut (Pins1/4/5)
Rewired: Pin6 to Fet-Gate (red wire)
MCU+ is already connected to V+out
Rewired: MCU- to GND
MCU- of the original driver is connected to Fet-Source/PAM3. This did not work with the Attiny, it wouldn’t change modes.
Rewired MCU- to GND (black wire) and voila: 3-mode boost driver that did survive several 1AA and 2AA drains.
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The first Oshpark board HQB15 v1 successfully built.
2× 2AA and 3× 1AA (Eneloops) drained, about 200 mode changes, all good.
It’s a HQB15 de-luxe with Coilcraft inductor and high value capacitors.
Partlist with used values and the firmware in this post.
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Driver height with this inductor is 3.7mm (0.2mm less than with the FT inductor). Now take the new Oshpark 0.8mm boards and you’re down to 2.9mm. That’s 3.0mm less than a Nanjg110.
Enough space around the Attiny13a for the clip after driver assembly.
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I took the experience from building v1 (it’s really, really tight) and tweaked the design. I skipped sharing v1 and went straight to HQB15 v2.
All future Oshpark boards will be introduced in this thread.