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2,4 volts to 5 volts, any suggestions of a DC-DC?
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2,4 volts to 5 volts, any suggestions of a DC-DC?

by casainho on Wed May 28, 2008 3:44 pm

Hello :-)

I want to add USB to the circuit, using a more recent MCU from Atmel that have USB, the AT90USB162.

The AT90USB162 needs a higher voltage, more than 2,4 volts, to have USB working. I tried using an DC-DC IC but I couldn't put it working... so I am asking for any suggestions, for having 5 volts and about 28mA at output.

I did draw the schematic and made power calculations, here:
http://code.google.com/p/bicycleledpov/wiki/PowerStage

Thank you.
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by kayrock66 on Thu Jun 05, 2008 10:56 am

My suggestion is to ditch the DC-DC converter idea. Batteries will do exactly what you need but more simply and higher in efficiency. If you need more than 2.4V for USB use 3 or 4 cells. depending on if you plan on running alkaline (1.5V) or ni-cd (1.2V) batteries.
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by casainho on Thu Jun 05, 2008 7:29 pm

kayrock66 wrote:My suggestion is to ditch the DC-DC converter idea. Batteries will do exactly what you need but more simply and higher in efficiency. If you need more than 2.4V for USB use 3 or 4 cells. depending on if you plan on running alkaline (1.5V) or ni-cd (1.2V) batteries.

Thank you. Yes, +5 volts just for AVR MCU with working USB peripheral.
I want to have less batteries to have a light and smaller device, also I would like to work with DC-DC IC's since I want to learn doing this project and DC-DC's looks like a must way to use MCU's with 1 or 2 NiMh cells.

But in the end I can use 2 NiMh in series for LED's + a third one (button size ??) in series to get 3.6 volts for the MCU. Who knows... ?? :)

I asked a few days ago for samples from Maxim-IC, for the same MAX used on Minty Boost and for another that just needs coil + capacitor...

I received today my AVR-USB-162 development board from Olimex and I did a few hacks in USBtoSerial program from MyUSB library and I got it working, but turning on the LED when I send value "1" to serial port and off the LED when I send "0" - It also send back to serial port the same vale sent before. Here some images (from GNU/Linux Ubuntu on my Asus eee pc 701):

Image

Image

It were very quick to install and use the dfu-programmer and avr-gcc on GNU/Linux Ubuntu!!
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by macegr on Thu Jun 05, 2008 7:58 pm

Do not put a button cell in series with larger batteries.
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by kayrock66 on Thu Jun 05, 2008 8:04 pm

One of the issues you'll have to solve with a DC-DC converter is the quiescent current. The SpokePOV sleeps very nicely using only tiny amount of battery power. With a DC-DC converter you don't have this option by conventional means.

Explain why weight is an issue. If you have a symmetric configuration of display boards the weight shouldn't matter. If weight really does matter, consider using AAA cells instead of AA.

Its nice if you can use all the same type of battery, and rechargeable that way you can don't have to keep on flipping out your wallet to use the display. You are free to configure images with lots of LEDs on running at high brightness.
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by casainho on Fri Jun 06, 2008 10:36 am

macegr wrote:Do not put a button cell in series with larger batteries.

Why not? is there any problem?

kayrock66 wrote:One of the issues you'll have to solve with a DC-DC converter is the quiescent current. The SpokePOV sleeps very nicely using only tiny amount of battery power. With a DC-DC converter you don't have this option by conventional means.

Okok, I must try and discover - thank you :)

kayrock66 wrote:Explain why weight is an issue. If you have a symmetric configuration of display boards the weight shouldn't matter. If weight really does matter, consider using AAA cells instead of AA.

Weight and size are always important for me. For example, I have a small bicycle of 20''. Also I would like to have something on transparent plastic and with white PCB.

kayrock66 wrote:Its nice if you can use all the same type of battery, and rechargeable that way you can don't have to keep on flipping out your wallet to use the display. You are free to configure images with lots of LEDs on running at high brightness.
Also rechargeable batteries are green, earth friendly ;) :)

In the end, summing up the size of the capacitor + coil + DC-DC ic, a small battery can be a better choice... I will try, discover :)
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by casainho on Wed Jul 02, 2008 5:49 pm

kayrock66 wrote:One of the issues you'll have to solve with a DC-DC converter is the quiescent current. The SpokePOV sleeps very nicely using only tiny amount of battery power. With a DC-DC converter you don't have this option by conventional means.

Sorry for my bad understand of English language - what do you mean by "quiescent current"??

I have tested the DC-DC which is the same as Minty Boost - thanks Lady Ada :-)

Here is some pictures:
Assembled circuit:
Image

Here are the results on oscilloscope, with 100mA output current - channel 1 on Vout and channel 2 on positive side of schottky diode:
Image

More info here:
http://code.google.com/p/bicycleledpov/wiki/PowerStage
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by kayrock66 on Tue Jul 08, 2008 11:46 pm

Quiescent current is the amount of current that the DC-DC converter will take for itself even if the uC is sleeping. This will discharge your battery.

You can only get away with 2 cells for the LEDs if you will only have red or yellow LEDs. I think people can see the superior coolness of throwing in green and blue LEDs and what they can do together. So if you need the extra cell for the full color, use it for your uC and get rid of the switcher.
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by casainho on Wed Jul 09, 2008 2:58 am

kayrock66 wrote:Quiescent current is the amount of current that the DC-DC converter will take for itself even if the uC is sleeping. This will discharge your battery.

You can only get away with 2 cells for the LEDs if you will only have red or yellow LEDs. I think people can see the superior coolness of throwing in green and blue LEDs and what they can do together. So if you need the extra cell for the full color, use it for your uC and get rid of the switcher.

Thank you.

I need at least 3,3 volts, preferable 5 volts, for MCU because of his USB functionality.
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by kayrock66 on Thu Jul 10, 2008 12:50 am

And what a happy coincidence that you need 3.3V preferrably 5V for driving blue and green LEDs.
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by casainho on Thu Jul 10, 2008 4:37 am

kayrock66 wrote:And what a happy coincidence that you need 3.3V preferrably 5V for driving blue and green LEDs.


Well, we changed to 3.3volts for MCU, sensor and memory - because we changed from 256Kb EEPROM to 8Mb DataFlash. DataFlash of 8Mb is even a bit more cheap than that 256Kb EEPROM.

So, the advances to Lady Ada POV is the USB connection on MCU and DataFlash of 8Mb (or 16, 32Mb, etc).
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