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Topic: Arduino pro mini v5 on-board MIC5205 150mA LDO Regulator (Read 6421 times)previous topic - next topic

Wasferd

Nov 21, 2015, 10:14 pmLast Edit: Nov 22, 2015, 04:20 am by Wasferd
I am currently working on a hand prosthetic and am developing a wearable wristband to read emg signals. The wristband contains the following:

1) Arduino Pro mini 5V ( Typical supply voltage: +5.0 V, Typical supply current: 10-25 mA)

2) Transmitter Module ( Typical supply voltage: +5.0 V, Typical supply current: 03-10 mA)

3) Myoware muscle sensor ( Typical supply voltage: +5.0 V, Typical supply current: 09-14 mA)

I am currently looking for a battery to power these components. The battery needs to be as small and as light as possible. It also needs to be rechargeable. There is no minimum operation time due to the project being a prototype, however, the longer the duration the better. I am currently looking at the s 200mAh 2S 7.4v 20C LiPo Battery ( http://www.overlander.co.uk/batteries/lipo-batteries/eflite-umx-beast-type-lipo-battery.html )

QUESTION 1) Will this battery work fine with the components mentioned above?

QUESTION 2) will it work for roughly hours as I calculated?

0.2 Ah /(25 mA+10 mA+14 mA)= 4 h

QUESTION 3) looking at the Arduino on-board voltage regulator (http://www.micrel.com/_PDF/mic5205.pdf) I calculate that there will be 0.379 W power dissipation is the value correct?

Pd=(7.4 V-5 V)*150 mA + 7.4 V *2.5 mA = 0.379 W

QUESTION 4) I also calculate that the voltage regulator temperature rise will be 83.83 C is the vale correct and is it normal or do I need a heat sink?

TempRise= 0.379 W*220 = 83.83 C

somedude

4.8V batteries may be smaller and more suitable for your project. Just a thought.

Wasferd

#2
Nov 21, 2015, 11:19 pmLast Edit: Nov 22, 2015, 04:20 am by Wasferd
Hey,
So you reckon powering the mini with 4.8V is better than using a 7.4V?

westfw

Quote
QUESTION 3) looking at the Arduino on-board voltage regulator (http://www.micrel.com/_PDF/mic5205.pdf) I calculate that there will be 0.379 W power dissipation is the value correct?

Pd=(7.4 V-5 V)*150 mA + 7.4 V *2.5 mA = 0.379 W
No, because you're not actually using 150mA.  And the 7.4V is "nominal" for a 2s LiPo pack (more like 8.4 initially.)
so, more like (worst case): Pd=(8.4 V-5 V)*(25 mA+10 mA+14 mA) + 8.4 V *2.5 mA

You might be a lot better off using a 1S LiPo and a boost regulator to get 5V, since a boost regulator will give you 80+% efficiency, while the linear step down is worse than 50%...

Wasferd

Yes, that should last a few hours per charge. Maybe 4 to 5.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Wasferd

Would  I need a PCB for the LiPo battery or is that unnecessary?

Not needed, just the connector.
For example, this remote control use a 3.3V/8MHz Promini running from a 1000mAH LiPo that is tiewrapped to the bottom of the card. A Max1811 (not plugged in here) is used to charge the battery from a 5V source (such as USB).
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#8
Nov 22, 2015, 06:17 amLast Edit: Nov 22, 2015, 06:18 am by CrossRoads
Here's the circuit
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Wasferd

#9
Nov 22, 2015, 06:40 amLast Edit: Nov 22, 2015, 06:43 am by Wasferd
But the battery datasheet says "Never discharge Li‐Po battery below the Lowest Discharge Voltage 3v per cell"

and the voltage regulator data says "takes an input voltage from 2.7 V to 11.8 V and increases or decreases the voltage to a fixed 5 V output'

Thus wouldn't the Voltage regulator discharge the battery to 2.7V causing irreversible damage which will deteriorate the battery performance and cycle life ?

https://www.pololu.com/product/2123
http://www.overlander.co.uk/fullymax_warning_sheet_li_poly.pdf

If you look at the schematic, you will notice I am powering the promini via the VCC pin, not Raw, so the onboard regulator is bypassed. The battery never sees more than 4.2V from the max1811 charge control chip.
The promini goes into power down sleep mode after waking up from a button press and transmitting the character via virtualWire library.
The battery lasts about a month between charges, when I notice that it is not sending anymore I plug it in to charge it.
A battery disconnect transistor would probably be good to keep the battery from overdischarging.
At the same time, it's been running like that since ~Jan 2011. Maybe battery life has been degraded some, I don't monitor it all that closely.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Wasferd

I also intend to power through the VCC pin bypassing the linear voltage regulator.
So Ill have the LiPo battery connected to an external switching voltage regulator connected to the VCC pin. The external voltage regulator I have been referring to will discharge a battery to 2.7V which is smaller than the limit of >3V LiPo cell discharge.  Perhaps I am misunderstanding something.

You'll have the battery connected to the input of a switching regulator, with nothing to stop the regulator from overdischarging the battery?  Yes, that could lead to battery issues.
You need a part like this to disconnect the battery from the load
https://www.sparkfun.com/datasheets/Prototyping/tps61200.pdf
Values here may need adjusting to meet 3V instead of something lower
https://www.sparkfun.com/products/10255
You need a battery charge control circuito to charge the battery still.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Wasferd

#13
Nov 22, 2015, 07:48 amLast Edit: Nov 22, 2015, 07:54 am by Wasferd
The two components seem rather complex. Is there no simpler solution to breaking a circuit when battery input voltage is lower than a set limit?

For example will this PCB disconnect the circuit at 3V ?
Over Discharge Protection   Over Discharge Detection Voltage       2.5±0.063V
Over Discharge Release Voltage           3.0±0.075V

http://www.all-battery.com/protectioncircuitmodulepcbfor37vli-polymerbattery15alimit-pcb1s.aspx

For charging the Battery can't I use something as simple as this ?http://www.overlander.co.uk/chargers/lipo-battery-balance-chargers/overlander-rc3-lipo-charger.html

Paul__B

The two components seem rather complex. Is there no simpler solution to breaking a circuit when battery input voltage is lower than a set limit?
Probably not.

Disconnecting a battery below a certain voltage is a particularly complex problem, since the circuit which does this must draw no current once disconnected, but draw no current when connected either as clearly that would actually discharge the battery - the very thing you need to prevent.

This rules out for example Zener diodes as threshold references; the entire circuit must be CMOS.

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