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31  Using Arduino / General Electronics / Re: 2N7000 as power swtich ? on: October 10, 2013, 04:07:06 am
Hej Nick, that's pretty impressive and very encouraging.  Do you know how long the AAs last for in the field?  I'm looking forward to getting my tests going again to see if I can shave a mere 393uA of my baseline :-)
32  Using Arduino / General Electronics / Re: 2N7000 as power swtich ? on: October 09, 2013, 04:23:33 pm
Hi Nick,

Thats just what I was looking for, thank you.
May I ask how you deal with restarting the SD card in code each time you use it as powering off presumably means reinitialising?
Was the 6-7 uA in powerdown a measured value?  very impressive - I'm currently running at 400uA !!!  I need to get this lower :-)
33  Using Arduino / General Electronics / Re: 2N7000 as power swtich ? on: October 09, 2013, 12:28:46 pm
Thanks Mike,

Is there any advantage of going for a P channel FET over say the circuit below (which may also be wrong?) in terms of keeping this a really low power switch?  Maybe the question should be more like: what is the best way to switch periferals on and off with low power consumption as the main aim?
34  Using Arduino / General Electronics / 2N7000 as power swtich ? on: October 09, 2013, 10:45:47 am
Hi, I am looking to switch an SD card on and off to allow maximum power saving in SLEEP mode and wonder if using a 2N7000 Mosfet to switch the SD 3V3 supply via arduino pin D2 is the best bet?

My circuit looks like this which may be wrong, any pointers appreciated.


35  Using Arduino / Storage / Re: SD Card - how to reduce the power consumption? on: September 19, 2013, 03:47:55 pm
Evenin' all,

I'm just trying to do the same - that is get the power right down in between my data logs which occur every 5 mins.

The best I can do at the mo is about 500uA in sleep mode (the arduino bit accounts for 22uA) so I'm wondering if I need to do anything more than close the SD file to get the SD card to sleep?... or perhaps its my SD card - any recommendations for nice sleepy SD cards and any difference between micro SD and full size?

Any code snippets to illustrate would be great :-)
36  Using Arduino / Networking, Protocols, and Devices / Re: Simple ACK & CRC over Serial - HOW TO? on: September 15, 2013, 12:05:27 pm
FAB, thanks Paul,

.... just need to find out how to calculate a CRC values based on the contents of the STRUCT data packet and I think I have enough to try some tests :-)
37  Using Arduino / Networking, Protocols, and Devices / Re: Simple ACK & CRC over Serial - HOW TO? on: September 15, 2013, 11:06:52 am
Thanks Paul,

So in my data packet I would add 1 value for CRC.... :

struct DATA{
  int sensor1;
  int sensor2;
  int CRC;
};

Then the logic would go something like if CRC=CRC then SEND ACK else RESEND?

How would I best calculate a CRC value?  Is there a nice code snippet/library I can dip into?
38  Using Arduino / Networking, Protocols, and Devices / Simple ACK & CRC over Serial - HOW TO? on: September 15, 2013, 10:31:31 am
Hi all,

I am just looking to understand ACK and CRC over a Serial connection and wondering if anyone can explain what I need to make happen in each case and maybe even show how it might be done?

The aim is for a data package built with STRUCT to be checked for correctness with CRC and then Acknowledged as recieved successfully.

Sorry for the simple question, just dupping my toe into this stuff :-)
39  Using Arduino / General Electronics / Re: High side & Low side swiching? on: June 21, 2013, 08:52:23 am
FAB - I will get some on order and give it a try - thanks for helping me out with this basic question :-)
40  Using Arduino / General Electronics / Re: High side & Low side swiching? on: June 21, 2013, 04:02:27 am
Thanks again - as I would like to move this to PCB eventually an SOT23 package option would be ideal, may I ask if this one is suitable for the schematic in question too?

http://www.nxp.com/documents/data_sheet/BC807_BC807W_BC327.pdf

..... or perhaps this one which seems to be a replacement for the above:

http://www.nxp.com/documents/data_sheet/BCW29_BCW30.pdf

41  Using Arduino / General Electronics / Re: High side & Low side swiching? on: June 20, 2013, 02:52:41 pm
Wow, that was quick, thanks CrossRoads.

The current in question is only 45mA... 60mA MAX.  So it look like this circuit will work if I swap out the resistor to 1K and change the transistor to a PNP?  Would you be able to recommend a part number - I will need to go out and buy some :-)
42  Using Arduino / General Electronics / High side & Low side swiching? on: June 20, 2013, 02:37:50 pm
Hi,

May I run this by you good folks before I connect up and fry something :-)

Baiscally I would like to switch the backlight LED on an LCD on and off via a transistor and I'm not to sure about the high/low side switching thing.  The LCD LED in question shares the GND with the rest of the display so the only option open is high side switching - below is the circuit I propose but not sure it its correct?  The transistor in there at the mo is a BC817 NPN : http://www.nxp.com/documents/data_sheet/BC817_BC817W_BC337.pdf (the symbol I have used if for a PNP - sorry about that).
43  Using Arduino / General Electronics / Anyone got a Keithley 6517B High Resistance meter? on: May 15, 2013, 05:01:58 am
Hi,

I have been searching high and low for someone with a Keithley 6517B High Resistance Meter who might be able to help out by taking 10 resistance measurements of some SMD resistors we have ranging up to 50G ohm?  If anyone has one or knows who has it would be great to hear :-)

Many thanks.
44  Using Arduino / Networking, Protocols, and Devices / Switching I2C power off to save battery? on: May 13, 2013, 04:19:31 pm
Hi,

I recenlty tried using the P82B715 http://www.nxp.com/documents/data_sheet/P82B715.pdf I2C extender chip to get cable lenghts of about 20 metres - worked great :-)

The problem I found was that the power drain for my battery operated device was just too high to be useful so wondering if anyone has experience of turning the power supply (in my case 3V3) to the I2C bus off between reading the sensors every 5 minutes?  I guess I can use a transistor switched by a digital pin to do this as the power comsumption is more than 20mA but I thought I might ask for some advice before heading down a dark alley :-)

The questions I have are:

- Is the P82B715 the best way of extending cable length for a low power application?
- If a transistor routes sounds sensible would I be best switching the low side or high side and with which transistor to really keep power consumption to a minimum?
- If I turn the power to the I2C sensors off will I need to re-initialise them after powering on again or may I just continue to call for data as I would have done without powering off?
- Anyting else I should keep in mind when doing this?
- I'm guessing this has been written about somehwere but cannot find anything - anyone have a nice link?

Thanks for any thoughts - cheers
45  Using Arduino / Programming Questions / Re: A more elegant way to read multiple TMP275 sensors via I2C on: May 08, 2013, 05:11:19 pm
4 sure :-) ... I'm slow learning how to speak NiceDuino rather ClunkDuino....
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