Another Garden Light - This time with Hope(RF)
- Thread starter microman171
- Start date
microman171
Member
Expecting them tomorrow may be being a bit optimistic, but it would absolutely great if they did arrive!
I've got that enable pin working, 20uA is not much at all!
I performed a test on the PICAXE, and my low power record stands at 200uA... I've heard of 2uA! Obviously I'm doing something wrong... All my IO pins are pulled either high or low by 10k resistors, does it make a difference if they are high or low?
I've got that enable pin working, 20uA is not much at all!
I performed a test on the PICAXE, and my low power record stands at 200uA... I've heard of 2uA! Obviously I'm doing something wrong... All my IO pins are pulled either high or low by 10k resistors, does it make a difference if they are high or low?
westaust55
Moderator
Divine intervention may see you get them on Sunday
Otherwise wait for the postie/courier on Monday
EDIT:
A bit of the D.I. might also get my home access to the forum working again as well.
Do not know exactly what happens but from time to time I lose forum access at 9pm WA time for several days. Latest "abstinence" started on Wed night.
I can still access Rev Ed's regular website and anything else - just the PICAXE forum become inaccessible to me for from 3 to 7 days.
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WestAust55- it could be related to the cricket?
MM: Those caps. in fact posted yesterday aft (8th). The 08M BOD (Brown Out Disable) command => DISABLEBOD is your microAmp mate, as a normal SLEEP (as you've found) is indeed still pretty greedy. Deactivating BOD like this makes it possible to keep an 08M alive down to 1µA at 1.3 volts. However associated devices may not be happy with such a low supply of course!
MM: Those caps. in fact posted yesterday aft (8th). The 08M BOD (Brown Out Disable) command => DISABLEBOD is your microAmp mate, as a normal SLEEP (as you've found) is indeed still pretty greedy. Deactivating BOD like this makes it possible to keep an 08M alive down to 1µA at 1.3 volts. However associated devices may not be happy with such a low supply of course!
Stan is abs right about disabling BOD will reduce current.
Maybe disabling ADC module after a Read will help too?
A couple of things.
1. There is a reason for having Brown-Out Detect - noting that in other PICs they have changed the name to Brown-Out Reset.
When a PIC starts edging below it's comfortable operational voltage funny things can happen in registers.
Sometimes unpredictably. This can mess up your programme.
So, if disabling BOD/BOR you need to be confident that the voltage will NEVER drop too low - even briefly.
2. You use 2 ADCs. How will you be confident that the supply VOLTAGE to PICAXE is at the correct level for accurate ADC readings?
In circuits with an unpredictable supply you normally have a reference.
With your low duty cycle combined with the perfect (according to Stan) Kiwi sun I would have thought that you could arrange the power supply to give a constant voltage (?).
Personally, with that duty cycle, I think I'd just change things a bit and bung in a lithium battery and be damned (by the Greenies).
Maybe disabling ADC module after a Read will help too?
A couple of things.
1. There is a reason for having Brown-Out Detect - noting that in other PICs they have changed the name to Brown-Out Reset.
When a PIC starts edging below it's comfortable operational voltage funny things can happen in registers.
Sometimes unpredictably. This can mess up your programme.
So, if disabling BOD/BOR you need to be confident that the voltage will NEVER drop too low - even briefly.
2. You use 2 ADCs. How will you be confident that the supply VOLTAGE to PICAXE is at the correct level for accurate ADC readings?
In circuits with an unpredictable supply you normally have a reference.
With your low duty cycle combined with the perfect (according to Stan) Kiwi sun I would have thought that you could arrange the power supply to give a constant voltage (?).
Personally, with that duty cycle, I think I'd just change things a bit and bung in a lithium battery and be damned (by the Greenies).
microman171
Member
I actually have a lithium battery, but it's only 3.3v, and the hope module (and many other wireless modules) dislike anything other than 5v...
Andrew has been doing some tests with a 4700uF capacitor, and he is adamant that the 4700uF capacitor is enough to run a HopeRF + PICAXE combo for about 1 minute without a solar module... The device runs on the 4700uF alone! I have got the Brightspark's Hitech Competition in about a week, so I will probably go with what works for now, but as soon as that is over I'll have plenty of time to try this out...
How do I turn off the ADC modules?
I have got DisableBOD turned on, but I never realised it was bad...
With the regulated idea... If I had a bank larger than 5v, then it would be a possibility... I have a 16v 4700uF capacitor, so I could whack a 5v regulator on that...
Andrew has been doing some tests with a 4700uF capacitor, and he is adamant that the 4700uF capacitor is enough to run a HopeRF + PICAXE combo for about 1 minute without a solar module... The device runs on the 4700uF alone! I have got the Brightspark's Hitech Competition in about a week, so I will probably go with what works for now, but as soon as that is over I'll have plenty of time to try this out...
How do I turn off the ADC modules?
I have got DisableBOD turned on, but I never realised it was bad...
With the regulated idea... If I had a bank larger than 5v, then it would be a possibility... I have a 16v 4700uF capacitor, so I could whack a 5v regulator on that...
Didn't you say earlier that your solar panel open circuit produced a bit over 6V?
Well, that'll be (arguably) the highest voltage that your capacitor will ever achieve.
A voltage regulator needs a bit of voltage 'headroom'. Some of the very low dropout ones will be a few tens to a few hundreds of mV e.g. the LPC2950 which I have mentioned.
Once your capacitor voltage droops below 5V+DropoutV then the 5V output from it will droop, making accurate ADC measurements in your proposed circuit invalid.
(And maybe upset Hope too?)
So, you'll have to look into that a bit more.
There are oodles of RF modules that work at 3V, and powering it all with a 3V LPC reg would give loads of headroom and time, but if you're stuck with the Hope then you may have to do a bit more thought.
Or can that inverter be tweaked to 'up' the voltage to 9V for example?
Or could you have a solar-panel+cap // battery dioded switchover as a backup?
Try and build in some 'spare' for worst-case. Quite a lot of options.
I'm sure you and the others will get it sorted.
ADC Module.
haven't got data sheet to hand but it's usually ADCON0.0 on the older/smaller PICs.
Check Microchip Data Sheet.
Others may be able to let you know whether POKIng this can upset anything else.
Well, that'll be (arguably) the highest voltage that your capacitor will ever achieve.
A voltage regulator needs a bit of voltage 'headroom'. Some of the very low dropout ones will be a few tens to a few hundreds of mV e.g. the LPC2950 which I have mentioned.
Once your capacitor voltage droops below 5V+DropoutV then the 5V output from it will droop, making accurate ADC measurements in your proposed circuit invalid.
(And maybe upset Hope too?)
So, you'll have to look into that a bit more.
There are oodles of RF modules that work at 3V, and powering it all with a 3V LPC reg would give loads of headroom and time, but if you're stuck with the Hope then you may have to do a bit more thought.
Or can that inverter be tweaked to 'up' the voltage to 9V for example?
Or could you have a solar-panel+cap // battery dioded switchover as a backup?
Try and build in some 'spare' for worst-case. Quite a lot of options.
I'm sure you and the others will get it sorted.
ADC Module.
haven't got data sheet to hand but it's usually ADCON0.0 on the older/smaller PICs.
Check Microchip Data Sheet.
Others may be able to let you know whether POKIng this can upset anything else.
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microman171
Member
I haven't tested the inverter voltage output... The last one I had was about 9v, and I imagine this will between 7v and 9v.
The open circuit voltage of the two solar panels wired in series in full sunshine was 6v, so I don't think charging the capacitor/s with that would be a good idea... Hence the inverter.
I'm not planning on this set up dropping below 5v. As if it does, a downward spiral begins, the HopeRF module tries to start, and so draws more current, but the voltage isn't high enough. Both the PICAXE 08M and the HopeRF give up at about 1v - 1.8v, where it stays steady.
The open circuit voltage of the two solar panels wired in series in full sunshine was 6v, so I don't think charging the capacitor/s with that would be a good idea... Hence the inverter.
I'm not planning on this set up dropping below 5v. As if it does, a downward spiral begins, the HopeRF module tries to start, and so draws more current, but the voltage isn't high enough. Both the PICAXE 08M and the HopeRF give up at about 1v - 1.8v, where it stays steady.
lbenson
Senior Member
Check out this thread for low current picaxe usage (pre-X2); Low-Power Battery Backup Reference Design: http://www.picaxeforum.co.uk/showthread.php?t=8353
microman171
Member
I followed some of the tips on your topic, and I now have an LED (via 22k resistor) running off a 4700uF capacitor. The PICAXE is running at 31KHz with no ADC and no brown out detection, the LED blinks every 8 or so seconds for 128ms. I'll see how long it lasts =)
I will definitely employ these techniques in the solar garden light. Thanks!
I will definitely employ these techniques in the solar garden light. Thanks!
microman171
Member
I was planning to swap back to 4MHz to transmit the serial data. I'll also re-enable ADC.
microman171
Member
That sounds good mate =D
@manuka: The capacitors arrived this morning (or last night...). I've wired two series LEDs across the individual capacitors, but I'm not sure if they work...
How would I do this with resistors? I have two 2.5v 1F capacitors wired in series, what resistors would I wire in (and how) to make sure the capacitors only hold 2.5v each?
@manuka: The capacitors arrived this morning (or last night...). I've wired two series LEDs across the individual capacitors, but I'm not sure if they work...
How would I do this with resistors? I have two 2.5v 1F capacitors wired in series, what resistors would I wire in (and how) to make sure the capacitors only hold 2.5v each?
BeanieBots
Moderator
Forget the resistor method of balancing. It will waste your valuable current.
Two LEDs in series might be a bit high for 2.5v caps.
Personally, I think for 5v, you should be looking at using 3 caps in series.
Also, I still have concerns about your PV open circuit voltage. If it is only 6v OC, then it will drop to about 4.5v when running at maximum effciency.
Combining all of the above and your requirement for a reliable 5v strongly suggests the use of THREE PV units and THREE caps to give sufficient headroom on voltage (ideally combined with a low quiesent, low drop-out regulator). Don't forget, you are using the caps as a resevoir FOR 5v. Hence, your stored voltage must be greater than 5v. The second you draw any power they will drop in voltage. If you only want to use two, then you should be looking at a 3v system. Not 5v.
Two LEDs in series might be a bit high for 2.5v caps.
Personally, I think for 5v, you should be looking at using 3 caps in series.
Also, I still have concerns about your PV open circuit voltage. If it is only 6v OC, then it will drop to about 4.5v when running at maximum effciency.
Combining all of the above and your requirement for a reliable 5v strongly suggests the use of THREE PV units and THREE caps to give sufficient headroom on voltage (ideally combined with a low quiesent, low drop-out regulator). Don't forget, you are using the caps as a resevoir FOR 5v. Hence, your stored voltage must be greater than 5v. The second you draw any power they will drop in voltage. If you only want to use two, then you should be looking at a 3v system. Not 5v.
microman171
Member
After removing the parallel LEDs, I found that I could get the capacitor voltage to about 5.7 maximum. Seems the inverter pumps the voltage to right where I need it... There is a voltage drop of about 0.3v, and this is all above the 5.0v minimum.
The actual inverter voltage is about 6.0 - 6.7 or so, so this must b he voltage drop you were talking about.
The actual inverter voltage is about 6.0 - 6.7 or so, so this must b he voltage drop you were talking about.
BeanieBots
Moderator
5.7v across two 2.5v (absolute max) capacitors
Hope you're wearing safety glasses!
Hope you're wearing safety glasses!
@BB,
Whilst technically you are correct at implying that the capacitors could explode because of the over-voltage, surely the chances are very slim given the low power available from the solar panels.
To overcome this potential hazard, simply put a diode in series from the solar panels to the caps.
Whilst technically you are correct at implying that the capacitors could explode because of the over-voltage, surely the chances are very slim given the low power available from the solar panels.
To overcome this potential hazard, simply put a diode in series from the solar panels to the caps.
BeanieBots
Moderator
@MPep, the potential power is already in the cap as stored energy.
A bit like saying if I fill a bucket with gunpowder only a sprinkle at a time the explosion won't be as great if I fill it slowly.
In reality, a super cap charged just over it's rating is only likely to develop a high leakage current, but either way, the cap WILL be destroyed over time.
A bit like saying if I fill a bucket with gunpowder only a sprinkle at a time the explosion won't be as great if I fill it slowly.
In reality, a super cap charged just over it's rating is only likely to develop a high leakage current, but either way, the cap WILL be destroyed over time.
microman171
Member
I'd better put some series LEDs back on then =)
Thanks for the tips.
Thanks for the tips.
microman171
Member
I installed a 5.1v Zener Diode.
It drops to about 4.95 after transmission, so there is plenty of capacity there!
It drops to about 4.95 after transmission, so there is plenty of capacity there!
BeanieBots
Moderator
The 5v1 will probably (quite leaky at 5v) save the caps from total over-voltage but make sure you have the LEDs fitted to protect them individually (which makes the 5v1 redundant anyway).
Also note that you are assuming the voltage will be the same across each cap. This might not be the case. 2*2.5v caps in series is a bit like two rechargeable batteries in series. When cell one is discharged to zero, cell two may still have a some charge left and force cell one into reverse polarity. Also during charging, cell one might reach full capacity before the other, so cell one could be overcharged by the time cell two is fully charged.
If you insist of using series supercaps, don’t charge them to max voltage. Leave a little headroom, say 1v. (Charge to 4v max). Or use some other method to ensure equal balance.
If you insist of using series supercaps, don’t charge them to max voltage. Leave a little headroom, say 1v. (Charge to 4v max). Or use some other method to ensure equal balance.
BeanieBots
Moderator
What Boriz says, but we're just going round in circles now!
This has already been clearly explained.
This has already been clearly explained.