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1  Using Arduino / Microcontrollers / Re: atmega328p being powered through AREF! on: September 28, 2013, 02:19:10 pm

I'm looking for a way to monitor the LiPo battery voltage without needing an extra IC.

The atmega is powered through a regulator as there are sensors on the board that require 3V. Hence, I thought of using the battery connected to AREF and comparing it to the 3V (via an analog pin). You're right though, on reading the data sheet, no pin should exceed AVCC/VCC +0.5V!

It's designed to have a very long standby time, so I'm loathe to use a resistor voltage divider to bring the voltage down (as it's always on!).

Any ideas?
2  Using Arduino / Microcontrollers / atmega328p being powered through AREF! on: September 24, 2013, 09:57:10 am
I'm using an atmega328p in a standalone project.

I've discovered that when a voltage (5v) is being applied to the AREF pin, the microcontroller powers up and operates! In fact it, puts out a little over 3v on the Vcc pins.

Is there a way to prevent this?
3  Using Arduino / Microcontrollers / Re: How to bootload/program an atmega328p at 1.8v on: December 09, 2012, 11:51:08 am
Perfect. I'm sure I'll forget the bootloader (or AVRStudio) to burn the fuses and end up scratching my head too. smiley-wink

Thanks for all the replies.
4  Using Arduino / Microcontrollers / Re: How to bootload/program an atmega328p at 1.8v on: December 09, 2012, 09:13:01 am

I actually hadn't realised that ICSP programming (without a bootloader) would be so simple. I think I'll just get a AVRISP mkII. =)

Out of curiosity, if I stick to using the Arduino IDE, I'm assuming that the fuses are only set by the IDE when burning a bootloader. Is that right? (I.e. fuses are not set when using a programmer to load a sketch.)
5  Using Arduino / Microcontrollers / Re: How to bootload/program an atmega328p at 1.8v on: December 08, 2012, 05:50:14 pm
Sounds like I might need to design my own programming board. =)

I think I need something along the lines of:
- an FTDI chip which allows logic level translation between 5V USB and 1.8V (e.g. FT230X)
- an 1.8V regulator and atmega328p

I believe this covers my two needs:
(1) to bootload - the FTDI talks via UART to the onboard 1.8V atmega328p which performs ICSP bootloading of the external microcontroller
(2) to load a sketch - the FTDI talks via 1.8v UART to the external microcontroller (the onboard atmega328p is not used)

Does that sound about right/anything I have missed?
6  Using Arduino / Microcontrollers / Re: How to bootload/program an atmega328p at 1.8v on: December 07, 2012, 06:38:47 pm
Alas it's a size sensitive design, so based on the TQFP-32.

I can't imagine I am the first to encounter this, yet I can't seem to find a solution out there...
7  Using Arduino / Microcontrollers / How to bootload/program an atmega328p at 1.8v on: December 06, 2012, 06:51:09 pm
I've designed a circuit around the atmega328p and a number of 1.8v devices. They are only tolerant of 2v max on the supply. When in operation it will use a single AA/AAA and boost converter to provide a constant 1.8v.

My question is - how do I bootload/program the atmega328p? All my previous circuits were 5v tolerant, so I could simply use an arduino to load the bootloader and then use a FTDI clone (both at 5v).

I don't want to add line level conversion to the circuit if I can help it! Is there an alternative/standard/simple way to bootload/program?
8  Using Arduino / LEDs and Multiplexing / Maximum Efficiency LED Driving for Bike Project on: March 23, 2012, 03:33:56 am
I'd like to build a bike light project. I plan to have two lights, one cree XML or similar powerful emitter at the front (1-200 lumens ish) adn a Seoul P4 for the rear (native red, 80 lumens). They both need slightly more than the 40mA an Arduino pin can provide (more like 3-700 mA!). I see a lot of these sorts of lights (and torches) use Li Ion batteries. I'd like to keep it simple and use AA/AAA rechargables.

Now for the questions!
(1) what's the maximum mA I can expect to be able to draw from AA/AAA x3 (in series for 3.6v)
(2) is 3.3v logic safe at 3.6v in gneral? Or am I pushing my luck?
(3) is there a simple, yet very efficient driver circuit for the emitters (I understand they need have the current controlled accurately). Note that I'd like to retain the ability to flash or PWM control the brightness

9  Using Arduino / General Electronics / Re: arduino project prototype conversion to final product on: March 02, 2012, 01:46:33 am
I'm planning a similar conversion using my own custom PCB to house all the components needed for the project.

One item I'm stuggling with a little is the power. All my logic runs at 5v and I'd like to use USB for power. Looking at the schematic for an UNO R3, as far as I can tell the usb power goes through a resettable 500mA fuse and then a FDN340P mosfet. I don't really understand the circuit - is the mosfet just used for switching in 5v (via a regulator) from the power jack?

Or perhaps to put it another way, if I'm using a mains powered USB supply, can I feed that stright to the ATmega via a resettable fuse, or is it wise to add more circuitry (to smooth, regulate or protect)?

What is the function of the 100nF cap between the 5V and gnd (located near the VCC pin of the ATmega)?

Sorry for the noob questions, if there's a 5v power 101 page anywhere, do let me know! Thanks.
10  Using Arduino / Motors, Mechanics, and Power / New Power Shield - useful? on: February 22, 2012, 11:45:53 pm
I spotted this press release yesterday:

I think it looks very interesting as it's comparatively low cost. Assuming I understand it properly, a comparatively simple and small circuit could provide power for an Arduino board, plus a few high power (up to 5A at 5V) feeds for other use. All programmable via simple I2C.The downside is that it is only QFN packaged.

Is there a need for high power projects? I can imagine it would be fun for LED cubes and high power Cree like LEDs. Are there other projects that have been crying out for this sort of circuit? Just trying to work out if a shield would be popular enough to warrant getting made.
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