USB power?
- Thread starter Jamcof
- Start date
No, the PICAXE won't be damaged as long as the USB port is within specification with the exception of the 3V-only parts. Power cannot be supplied via an AXE027.
USB devices are supposed to communicate with the computer if they need more than 100mA of current, though in practice up to 500mA without enumeration is fine as long as an unpowered hub is not used and cheap power banks and the like just don't bother with enumeration. Multiple non-compliant devices plugged into unpowered USB hubs have been known to cause the polyfuses on the motherboard to become high in resistance permanently, often resulting in USB flash drives working fine and LED-encrusted input devices not.
USB devices are supposed to communicate with the computer if they need more than 100mA of current, though in practice up to 500mA without enumeration is fine as long as an unpowered hub is not used and cheap power banks and the like just don't bother with enumeration. Multiple non-compliant devices plugged into unpowered USB hubs have been known to cause the polyfuses on the motherboard to become high in resistance permanently, often resulting in USB flash drives working fine and LED-encrusted input devices not.
Okey thanks! I am trying to understand with my english skills what you are saying. So if I power up my chip with power bank (output 2A) will it be fine?
Power bank was an example of a product which often ignores the USB specification.
If your project draws less than 100mA, it's absolutely fine to power it from a computer USB port.
If your project draws less than 500mA but more than 100mA, it will usually be fine to power it from a computer USB port but it won't be compliant with the USB specification and mustn't be used with an bus-powered hub.
Yes, I use 5 Volt USB from a power bank for M2 and X2 PICAXE chips.
erco
Senior Member
Ha, check my minutes-old post at http://forums.parallax.com/discussion/163305/68-cent-powerbank#latest
erco
Senior Member
@jims: That's a 68 cent Powerbank, you supply the 18650 cell. Amazing value IMO, it charges the battery via a micro USB cable (included!) and also boosts the cell's 3.7-4.0V voltage to 5.0 volts to power/charge USB devices. Complete power management for a little robot I'm building, using that Powerbank as the chassis.
I use something similar to this:
Available for 67pence, including shipping. http://www.aliexpress.com/item/Breadboard-Power-Supply-Module-3-3V-5V-MB102-Solderless-Bread-Board-DIY-2012-New-3PCS/708949986.html Just make sure that you get a version that matches the size of breadboard you want it to fit. Otherwise your next order will be for some breadboard. Yes, I made that mistake.
Available for 67pence, including shipping. http://www.aliexpress.com/item/Breadboard-Power-Supply-Module-3-3V-5V-MB102-Solderless-Bread-Board-DIY-2012-New-3PCS/708949986.html Just make sure that you get a version that matches the size of breadboard you want it to fit. Otherwise your next order will be for some breadboard. Yes, I made that mistake.
premelec
Senior Member
@erco etc... I got some of the 18650 battery boxes and tested them - about 80 ohms load would turn them on and 330 ohms kept them on - and once on several seconds before they turn off... so an occasional current draw should keep 'em on... a nice cheap unit! [http://www.ebay.com/itm/121864067222 you referenced...] BTW they cutoff at about 4.2v charge also... with a taper charge took which took about 70% of the discharge time to recharge...
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I've picked up a couple of these 18650 boxes as well; they're great!
I'm wondering if I can do the following: (plan to wire it up and test possibly today)
Use the power box along with a 1f 5V super-cap...maybe a diode to keep the cap from feeding back into the power-box.
Have the PICAXE go into low-power sleep mode...wake up, take a quick temp reading, and go back to sleep...(all powered from the super-cap)...then, (after I determine how many times the super-cap can support that)...let's say for example, 5 times, on the 6th wake-up...fire up some LEDs to create enough current draw to trigger the power-box to turn on....super-cap recharges, and go back to sleep...wash-rinse-repeat...It would be fun to drop a picaxe off somewhere for a month of temperature readings or something, and power it all off of this nifty little box!
I'm wondering if I can do the following: (plan to wire it up and test possibly today)
Use the power box along with a 1f 5V super-cap...maybe a diode to keep the cap from feeding back into the power-box.
Have the PICAXE go into low-power sleep mode...wake up, take a quick temp reading, and go back to sleep...(all powered from the super-cap)...then, (after I determine how many times the super-cap can support that)...let's say for example, 5 times, on the 6th wake-up...fire up some LEDs to create enough current draw to trigger the power-box to turn on....super-cap recharges, and go back to sleep...wash-rinse-repeat...It would be fun to drop a picaxe off somewhere for a month of temperature readings or something, and power it all off of this nifty little box!
premelec
Senior Member
That might work for you or just use the 3.5v Li battery directly not through the up converter. A timed re-boot circuit added. Keep the charging circuit - perhaps tied to a small PV panel... The up converter lowers efficiency and many 'AXEs work fine on 3+ volts. If you use a diode it should be shottkey [sp?]...