The AMC7135 is a great little chip. Low Drop-Out and quite precise at controlling current. Unfortunately, None of the AMC7135 boards available were quite what I was looking for.
I wanted one that:
Was variable without PWM (Able to turn on 1,2,3,4,5,6,7, or 8 of the AMC7135s).
True Moon-Light Mode without PWM.
Was further variable using PWM if I wanted to use it, and had > 1khz PWM frequency.
Had the exact modes that I like, and none of the Modes that I don’t.
Allowed for complex modes. For instance, I like to have a mode that is 3 Seconds Off, 20mS On, 20mS Off, 20mS On, 20mS Off, 20mS On, Repeat. This works great as a beacon in case of emergency. It’s VERY identifiable from far away, but only has a 2% duty-cycle. Meaning a torch that lasts for an hour on high could run this beacon mode for at least 51 Hours Straight.
Had Mode-Memory that sets after turn-off rather than after turn-on.
Had Low-Voltage cut-off that would reduce brightness, but not completely leave me without light.
Had Temperature monitoring/throttling so that I wouldn’t burn up a light if I left it on.
Nothing off the shelf could do all this… So I made my own. Thought you all might like to see the results thus far.
Top Side:
PIC 20 pin QFN Micro Controller
4x AMC7135 380mA Current Regulators
20AWG Silicone wire for connecting to LED
Capacitor for Mode Memory
Very small current-regulator that allows me to turn on a NON-PWM Moonlight mode of 1mA
Bottom Side:
Additional 4x AMC7135 380mA Current Regulators.
Visible is the Temperature Sensor that will be thermal-epoxied to the Pill.
Cree XM-L U2 1A from Illumination Supply glued to the pill using Wakefield 155 Thermal Epoxy. (This stuff is the best you can buy.) Pill/Reflector from KaiDomain
Mounted Emitter. I’m really picky about the LED being centered. This one is perfect, and it will never move because it’s held in place using the Thermal Epoxy rather than Thermal Grease/Paste.
The cost would be outrageous compared to a KaiDomain 8x7135. The microcontroller and Thermal Sensor (Literally, just those two parts) cost more than the entire KaiDomain 8x7135, and that ships for Free!
Awesome, never worked with that particular uC but I know a lot of them do that. I haven’t done much circuit design actually. I wanted to possibly do that after school but took some MEMS classes and Physical Electronics and decided I wanted to get into actual device design more at the semiconductor/materials level, but I would still love to get into circuit design.
Love your work. But I must admit that I agree with you insofar as that the asking price of these would be a deterrent to most DIY'ers and they would therefore be for the select few willing and able to pay & being picky enough about drivers that they would also enjoy it. Which in turn would drive volumes down and prices up another notch.
That doesn't mean its not a good product at all.
BTW: Your build raises a few Q's in my mind.
Like what temperature have you set the step down at? And does you host actually get that how that you see a stepdown?
Thanks for showing us electronic noobs what CAN be done.
Unfortunately, you’re absolutely correct. I’d love to be able to offer some of these things for sale - but trying to build them at the same cost as a company in china who has very low labor costs and who makes thousands of them is just not possible. Realistically, I’d probably have to charge $25 for this driver by the time the parts, circuit board and labor were added up - and that’s if I could build/sell a hundred or two! I doubt many people would be willing to part with that much cash just to have a better AMC7135 driver…
To your questions;
I’ll probably set the step-down at about 50 degrees C - once the pill reaches that temperature, the driver will begin backing down the current to maintain that temp.
I don’t understand your second question about the host - could you rephrase?
Pretty much all modern microcontrollers can use a PWM pin as a regular output. Most uC’s, in fact, have multi-purpose pins which can be setup to use several different internal peripherals - it’s not uncommon to find a pin, for instance, that can be configured as a Digital Input, a Digital Output, and Analog Input, an Analog Comparator Input, and maybe even an Analog (DAC) output. It allows the chip manufacturer’s to cram a ton of options into a small pin-count device.
This particular PIC is a pretty standard PIC16, actually. Very easy to setup and there are TONS of code examples available on the net for this family.
I, too, would love to gain more of a background in semiconductor design/fab, but I’m too deep into circuit design to part ways with it now. The closest I’ve ever gotten to wafer design is some work on ASICs - and that’s probably as close as I’ll ever get.
