The zener diode is always in parallel with the capacitor on these drivers; I've never run it in series. This is because the zener diode is run reverse biased here so that it will only conduct current when it reaches its avalanche/breakdown voltage of 4.3v, where it starts to burn off the extra voltage.
Capacitor? The zener is put it on top of the resistor, isn’t it?
No. Both the zener & capacitor go from after the resistor to ground. They both tap into the power feed to pin 8 on the MCU.
Of coarse. I read it wrong, sorry about that… getting dizzy.
The resistor is to limit the amount of current the zener has to burn off. If you add the zener without the resistor it will fry in a few seconds.
Richard, I think it was your post in this thread that got me off track: Modding Qlite 7135 to Drive MT-G2?
The first photo you posted has the description “Here you can see the small diode on top of the resistor:”. It’s in fact on top of a capacitor.
Oops...yeah I was thinking one thing but wrote another; however, you could see the capacitor in the picture.
On the Oshpark 20 mm Zener Mod driver by Mattaus ( OSH Park ~) the zener appears to be in serial with the capacitor. Also the zener diode slot is larger than the capacitor. Why would one choose this design over the “traditional” zener mod with a smaller diode in parallel with the capacitor?
There is no way the zener will do its job if it is in series with the capacitor. The capacitor also won't be able to do its job. They both require a connection to the trace that goes to MCU pin 8 on one end, and ground on the other.
Zener goes from pin 8 to ground. Capacitor also goes from pin 8 to ground.
Aha… smacking my self in the head. That is indeed a parallel connection… I guess I’m not really cut out for this stuff… Oh well, glad people here are so friendly in helping out.
Things are starting to sink in… I hope…
It’s the off time capacitor (if present) that must be removed to flash, isn’t it? Removing the zener is not necessary?
Neither have to be removed. Only reason to do so would be if it physically blocks the clip. They flash fine.
I've done it several times. Fully assembled light, driver zener-modded and with off-time cap, remove driver from pill/head with LED wires still attached, flash, reinstall driver.
If there is no diode at D1, if it's bypassed with a jumper, then you cannot reflash unless you un-bypass it. The programmer tries to power the LED since there's nothing between pin 8 and B+, and B+ is the same as LED+. The ~200 ohm resistor used in place of the diode on a zener-modded driver is enough resistance that it won't screw up the programming.
Have you already tried to flash one and had problems?
Thanks for the info. I haven’t tried yet, but I will try it on one of my drivers from RMM with an off time cap: http://www.mtnelectronics.com/opencart/index.php?route=product/product&path=67&product_id=53
In the description he has written “You will lose reverse polarity protection, low voltage warning, and the ability to reprogram the MCU.” This kind of stuck, so I wanted to find out why the ability to reprogram is lost.
All I know is that I've never been able to get one to flash with the zener diode and 200 ohm resistor installed. I can flash it with the zener removed and 200 ohm in place, but not with the zener in place. I think that the zener basically short circuits the power to the MCU across the capacitor.
Richard, you might want to test again. I just pulled out one of the zener modded drivers (also with off time capacitor) I ordered from you and I could both read and re-flash it. The MT-G2 LED was disconnected if that makes a difference.
I don’t know if this has anything to do with it, but I’ve read about different voltage settings on the USB programmer. I have not had to touch mine, but as a zener is voltage related, the voltage setting on the USB programmer might have an impact.
My programmer would not work on any driver or even a bare attiny with the jumper set to 3.3v, even though others here say they use 3.3v but occasionally have issues. I have always used the 5v setting.
OT. The flashlight wiki should be updated. AVR Drivers - Flashlight Wiki
It shows pin 4 as GND on the usbasp programmer and 3 is NC. But I looked in the online manual for the programmer and it shows pin 4 as TX or RX, can’t remember exactly which and pin 3 as a GND. So I wired to pin 3 instead. And VCC isn’t even showed as connected on the wiki too. I got it all soldered up and got it working first try, but I kind of knew better even though rusty as hell. I think there’s some trolling going on. xd Takes me back to my hacking days where you would always get code that was bogus and you’d have to fix it over a couple days. That’s where the troll face comes from, it’s after 2 days of coffee and swearing, you finally have it.
But that would be something to update. I don’t know who updates the wiki. Unless you guys like it vague… hmm &trollface*
Interesting on the zener. I guess it doesn’t matter as long as the led is disconnected then I take it. I have to file that away in my cap.
As I have already said, mine flash just fine with the LED still connected and without removing the zener.
Even on the drivers that won't flash with the D1 shorted, disconnecting the LEDs (which glow dimly because they're being backfed by the programmer) still will not communicate.
I'm gonna have to eat some crow on this one. I tried to flash a couple of zener mod drivers last weekend and was able to do so...but I know that I tried several times before and could never make it work. Coincidence? Who knows.
Well it appears the setting is totally random then cause I’ve never got mine to work at 5v (tho I haven’t tried in months now), I always use 3.3.
I’m glad you posted this tho, I’m nearing the first ready to order version of my custom AVR_ZIF programmer I’ve designed and I wasn’t planning on having a jumper for setting it at all so I will definitely include that now.