Power supply and a better solution for protecting your Stamp
LoopyByteloose
Posts: 12,537
The BasicStamp is set up with a small·high efficentcy·regulator to be more efficent when used with batteries, but there are some trade offs.
These on-board·regulators have a narrower range of useful voltage (from 6 to 9 volts).
You may want to occasionally use a wall wart to save time and avoid recharging batteries, but the wall warts seem to be a risky solution as a 9 volt wall wart often puts out 12 or more volts and even a 6 volt wall wart may go over the 9 volts.
THERE IS A SOLUTION - Pre-regulation with a 7809 voltage regulator [noparse][[/noparse]rated at 1amp and input up to +35volts DC]
I built a little board which uses a 7809 to 'pre-regulate' the wall wart's output before it goes to the BasicStamp.· Though 30% or more of the power is wasted as heat, the unit has a greater operating range than the 'high efficency, low power regulators' and brings high end up to +35 volts DC!!!!
So you can mix 6 volt, 9volt, 12 volt, 15volt, 18volt, etc wall warts from out of your closet and still have a reliable and safe +9 volts delivered to your BasicStamp.
Of course, if you use high voltages, the device creates more heat and requires a better heat sink.· But, this is a little price to pay for avoiding the mistake of trusting the very questionable lable on the wall wart and having your project [noparse][[/noparse]including your BasicStamp] burn up.
In my case, I also put 50volt - 1000 mFd capacitor on the input side [noparse][[/noparse]because I happened to have one] and followed the spec of putting a 1mFd capacitor on the output.· IN this way, I have greater than needed ripple protection and hopefully some additional filtering from power line spikes
The whole unit took about an hour to build was much cheaper than buying a special pre-built regulated supply.· I am not sure if it will work well with a 6 volt wall wart [noparse][[/noparse]I don't have any], but I am sure that it won't hurt to try.
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G. Herzog in Taiwan
These on-board·regulators have a narrower range of useful voltage (from 6 to 9 volts).
You may want to occasionally use a wall wart to save time and avoid recharging batteries, but the wall warts seem to be a risky solution as a 9 volt wall wart often puts out 12 or more volts and even a 6 volt wall wart may go over the 9 volts.
THERE IS A SOLUTION - Pre-regulation with a 7809 voltage regulator [noparse][[/noparse]rated at 1amp and input up to +35volts DC]
I built a little board which uses a 7809 to 'pre-regulate' the wall wart's output before it goes to the BasicStamp.· Though 30% or more of the power is wasted as heat, the unit has a greater operating range than the 'high efficency, low power regulators' and brings high end up to +35 volts DC!!!!
So you can mix 6 volt, 9volt, 12 volt, 15volt, 18volt, etc wall warts from out of your closet and still have a reliable and safe +9 volts delivered to your BasicStamp.
Of course, if you use high voltages, the device creates more heat and requires a better heat sink.· But, this is a little price to pay for avoiding the mistake of trusting the very questionable lable on the wall wart and having your project [noparse][[/noparse]including your BasicStamp] burn up.
In my case, I also put 50volt - 1000 mFd capacitor on the input side [noparse][[/noparse]because I happened to have one] and followed the spec of putting a 1mFd capacitor on the output.· IN this way, I have greater than needed ripple protection and hopefully some additional filtering from power line spikes
The whole unit took about an hour to build was much cheaper than buying a special pre-built regulated supply.· I am not sure if it will work well with a 6 volt wall wart [noparse][[/noparse]I don't have any], but I am sure that it won't hurt to try.
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G. Herzog in Taiwan
Comments
I have a similar problem as Herzog describes right now.
I'm experimenting with the bluetooth EB500 units from Parallax. They take the power from Vin, before the regulator, and my 9 Volt wall wart is delivering 15 Volt and more at low loads. The maximum Voltage rating for the EB500 is 12 Volt.
There you are, I don't know at which voltage the EB500 will be fried. But I know it is too expensive equipment to try
My solution in this particular case is to put a shunt resistor over the power supply to lower its voltage.
Regards,
Klaus
The shunt resistor requires you do the math for each specific case and in some cases you must have an inventory of higher wattage resistors.
I have many componets that are not regulated that will take 9 volts (like the 555 chip and DC motors), some components with their own regulated motherboards, and some [noparse][[/noparse]such as the BasicStamp] with an attached regulator. At times, it is hard to recall which specification belongs to which. And it certainly is not easy to read the chip lables [noparse][[/noparse]as they are getting smaller and smaller] or to spend time to Goggle a fact sheet.
Additionally, some people love to insert a diode for polarity protection, but seem to forget the 0.7 voltage drop that all diodes cause [noparse][[/noparse]so the regulator may say it needs only 6 volts, but you must add at least another 0.7volts to the input to overcome the diode]
You could add a series of diodes to the wall wart instead of a shunt resistor, but one would have to be built for each wall warts output.
The BSP24/40 Demo Board says '6-9 volts' input. Should I just ignore the lable and try 18 volts? Are all the voltage regulators on all the Stamps the same?
At least this way, I have some idea of what might need the 9volt limit and what does not. And, I don't have to keep building custom power supplies as the projects evolve. I can provide a temporary, safe solution until I have finished benching the project and know all its power requirements. If I need another pre-regulator, I have a standard design.
And, the secondary purpose is allows me to conviently grab assorted freebie, old wall warts [noparse][[/noparse]mine range from 300ma to 2amps output and from 7.5volts to 18volts] and not keep buying and recharging batteries as my projects increase in number.
This becomes a kind of modular standard that allows one to quickly design, build, and test. I suppose that I will need to buy a 3amp 7809 or built a more complex regulator to really complete the kit.
Incidentally, it looks as though the 7809 requires 11 to 11.5volts minimal input. Neither a 7.5volt or 6volt wall wart reaches that high (I think the 7.5volt is reading about 10.1).
And, the 1000uF capicitor is quite useful brings the low side of the input ripple up to a higher level than say a 50uF. Apparently, it the bottom of the input ripple is below the minimum input of the regulator, it does not functon properly.
Having worked with BasicStamps for several months now, I find that I need to have 2, 3, or more Stamps operational on different boards to pull everything together.
Let say one is for the final robot itself, another is to test and comprehen new devices to be added on and their related code (without having to disrupt my robot), and the third one is for making sure I have not 'fried' one of my Stamps (this one does 'Hello world' and blinks LEDs on all pins). I discovered that those 9 volt Nicads [noparse][[/noparse]which I thought I could regularly use to safe power sources] only put ot 160 to 200 maH, so they have been interrupting work in progress and going back into the charger daily.
AND FINALLY, if I do take a destructive voltage spike [noparse][[/noparse]we have a lot of tropic lightning here] through the 120VAC, it has to work through the 9 volt pre-regulator before it can get to more expensive components.
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G. Herzog in Taiwan
Is your wall-wart a 'Regulated'/'stabilized' one?
(These have internal regulators, not just a rectifier and capacitors...)
If not, I suggest that you just bin it and buy a good one instead...
Most wall-warts used with the BOE and stamp applications are 'unregulated', (in other words, NOT 'Regulated'). This has not caused problems for many-many BS2 users. A typical unregulated supply costs $7.00, and a regulated one can cost $25.00 or more. The on-BOE regulator is a 7805, which has no problems with using an un-regulated wall-wart.
Now, it sounds like G. Herzog in Taiwan has worse power-main problems than most U.S. BOE users, so perhaps his 'pre-regulator' approach makes sense in his application. It seems overkill to me -- I would have thought a single 7805 would have sufficed -- but it should certainly work.
Also, he's choosing to use the on-BS2 regulator to power the BS2 from Vin -- which implies to me he has some other need for a clean 9-volts. Or maybe he just doesn't know yet that you can power the BS2 from a 7805 regulated 5 volts applied to VDD, and bypass the Vin and on-BS2 regulator completely.
Cheers,
Jim
I use TI switching regulators on all my stamp projects for years. The input is 8 to 40 volts and as it is a switching regulator ther eis no waste heat generated. Use it just like a 7805 3 terminal device. I use them in niosy industrial CNC machines running off a 24 volt DC supply that is lots of times not even regulated. It shared this with big inductive solenods, mortors and drive contacors. I have not lost a Stamp yet to a Power problem.
It is $12 from Digikey (Part# PT5101A-ND), but if you really love your stamp, why not show it!!!
I put a 300 uf cap on the input and output to help out.
Make sure the voltage rating is two timed the DC input voltage.
The regulator is rated 1 Amp at 5 Volts. You can get Horizantal or vertical mounting. See the Digikey catalog. (And they are available elsewhere, its just I use DK about 99%·of the time.)
A simple solution and cheap insurance.
Alan Bradford
Plasma Technologies
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Sid Weaver
Do you have a Stamp Tester?
http://hometown.aol.com/newzed/index.html
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You must be kidding!
I must admit to having paid $60 for one, ONCE, but that was for a SWITCHED, regulated PSU capable of delivering up to 70W power from 15V to 24V, with an unregulated 12V(car system) input.
Like the TI part, though. Particularly as I plan to build some electronics stuff for my car...
Maybe I'll fix up a few PSU's for a friend of mine, too...
( http://home.no.net/naomij/index.html Nice boat, he's somewhere on the Kanari isles at the moment )
Where do YOU buy your 'decent, regulated wall-warts'?
There were a lot of reasons to go with the 'pre-regulator' idea.· Many of the ones that you all mentioned.
But additionally, I am still trying to decide between various more advanced regulators in future battery powered projects and I did notice that some· regulators and boards only have a range of 6-9 volts.· Cost is a big factor and this was very cheap AC source that will transfer over to a 6-9volt DC battery.· $12 regulators for hobby projects are a bit steep, but for continual AC service is seems good.
I am happy to see so much dialogue as it seems to be a valid concept for bench work with a lot of pros and cons for field use as well.· It was inspired by a lot of email on the old Yahoo web site in which people discovered the hard way that the wall wart voltage rating most often is much lower than the actual output.
I am also happy to know that there are some very good products available for hostile, noisy environments.·
Has anyone worked in along side an·arc welder?· Or, is that beyond feasible?
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G. Herzog in Taiwan
Post Edited (Kramer) : 12/29/2004 3:34:54 PM GMT
And yes, using a 7809 for a bench-top replacement for a 9-volt battery is really very clever.
All Electronics and Jameco both have some excellent (and inexpensive) regulated supplies. I bought 10 12v wall warts from All Electronics for $6.00 each:
http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-1213&type=store
Jameco has some good 3A 5V regulated wall warts for about $12.00.
Kenny
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Kenny Gardner
GAP Development Company
http://www.gapdev.com/
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