Forums

How to power my circuit.

Started by Daniel Pitts August 7, 2012
Hello,

So far, all of my circuits have had the power supplied by an Arduino 
(compatible) board.  I'm going to try to change the setup here a little, 
and design a circuit that has just an ATTiny in its place, but now I 
have to think about power supply.

The circuit I'm envisioning is going to have three Texas Instruments 
"TLC5916" constant-current sink's, powering one column of a multiplexed 
8x8 RGB led matrix. The circuit will also have an ATTiny85 (or ATTiny84, 
depending on a few things), and a 74HC238 (to select the row on the LED 
matrix).

Now, if I'm reading the specs right, I think I can power the whole thing 
on 3 AA batteries (4.5 volts). But if I wanted to have more robust power 
handling, I'm not sure what I want to do.  I'd like to try to keep the 
circuit cheap, and potentially have it powered by a wall socket or USB. 
I also don't have the time/money to etch my own PCB, so something that I 
can plug into my protoboard is preferable.

Is it just me, or is deciding on a power supply a relatively difficult 
problem, compared to other aspects of working on digital circuitry?

Thanks in advance for any suggestions!

--
Daniel.
On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

>Hello, > >So far, all of my circuits have had the power supplied by an Arduino >(compatible) board. I'm going to try to change the setup here a little, >and design a circuit that has just an ATTiny in its place, but now I >have to think about power supply. > >The circuit I'm envisioning is going to have three Texas Instruments >"TLC5916" constant-current sink's, powering one column of a multiplexed >8x8 RGB led matrix. The circuit will also have an ATTiny85 (or ATTiny84, >depending on a few things), and a 74HC238 (to select the row on the LED >matrix). > >Now, if I'm reading the specs right, I think I can power the whole thing >on 3 AA batteries (4.5 volts). But if I wanted to have more robust power >handling, I'm not sure what I want to do. I'd like to try to keep the >circuit cheap, and potentially have it powered by a wall socket or USB. >I also don't have the time/money to etch my own PCB, so something that I >can plug into my protoboard is preferable. > >Is it just me, or is deciding on a power supply a relatively difficult >problem, compared to other aspects of working on digital circuitry? > >Thanks in advance for any suggestions!
Just use a 5V wall wart. You can either get a mating connector for your board or just cut the end off and solder the ends to your circuit. The ones with switching regulators are probably the best bet because you'll be sure they're regulated. These are generally specified as 120/240V. Linear or T/R (junk) will be 120V only (in the US).
On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

>Is it just me, or is deciding on a power supply a relatively difficult >problem, compared to other aspects of working on digital circuitry?
s/deciding on a power supply/analog design/ -- Yes, although it can be a lot of fun. If you don't need portability then krw's suggestion of a regulated wall wart is spot on and by far the simplest. Do ensure that the output is actually regulated, though; some are not more than a step-down transformer with a diode bridge. -- Rich Webb Norfolk, VA
Rich Webb wrote:
> On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts > <newsgroup.nospam@virtualinfinity.net> wrote: > >> Is it just me, or is deciding on a power supply a relatively difficult >> problem, compared to other aspects of working on digital circuitry? > > s/deciding on a power supply/analog design/ -- Yes, although it can be a > lot of fun. > > If you don't need portability then krw's suggestion of a regulated wall > wart is spot on and by far the simplest. Do ensure that the output is > actually regulated, though; some are not more than a step-down > transformer with a diode bridge. >
Most tend to be switchers these days because switchers can be lighter, which matters in containerized shipping. Heck, there's an external "laptop" power supply with my wife's new cheap desktop. -- Les Cargill
On 8/8/12 5:27 AM, Rich Webb wrote:
> On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts > <newsgroup.nospam@virtualinfinity.net> wrote: > >> Is it just me, or is deciding on a power supply a relatively difficult >> problem, compared to other aspects of working on digital circuitry? > > s/deciding on a power supply/analog design/ -- Yes, although it can be a > lot of fun. > > If you don't need portability then krw's suggestion of a regulated wall > wart is spot on and by far the simplest. Do ensure that the output is > actually regulated, though; some are not more than a step-down > transformer with a diode bridge. >
Okay, that all sounds good for now, and that's the approach I'll take. Although, how do I verify if it is actually regulated or not? In any case, I would like to know more about how to work on this kind of thing in the future. For instance, I need to replace my sprinkler system panel, which uses 24V for the valve controls, but I'll probably end up using 5V or 3.3V ICs for most of the rest of the circuit. Also, some idea's I had for projects require higher voltages. I'd be interested in creating a Geiger Counter, for instance. I'd also like to play around with EL wire for a project. Both of those require much higher voltages. Basically, I'm self-taught here, and would like some guidance on how best to learn when/why to use various methods of power supply, and how to design/build those. Thanks again for all the advice, Daniel.
On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

>Hello, > >So far, all of my circuits have had the power supplied by an Arduino >(compatible) board. I'm going to try to change the setup here a little, >and design a circuit that has just an ATTiny in its place, but now I >have to think about power supply. > >The circuit I'm envisioning is going to have three Texas Instruments >"TLC5916" constant-current sink's, powering one column of a multiplexed >8x8 RGB led matrix. The circuit will also have an ATTiny85 (or ATTiny84, >depending on a few things), and a 74HC238 (to select the row on the LED >matrix). > >Now, if I'm reading the specs right, I think I can power the whole thing >on 3 AA batteries (4.5 volts). But if I wanted to have more robust power >handling, I'm not sure what I want to do. I'd like to try to keep the >circuit cheap, and potentially have it powered by a wall socket or USB. >I also don't have the time/money to etch my own PCB, so something that I >can plug into my protoboard is preferable. > >Is it just me, or is deciding on a power supply a relatively difficult >problem, compared to other aspects of working on digital circuitry? > >Thanks in advance for any suggestions!
I bought a relatively cheap switching supply from Marlin P Jones. It gets a lot of use with the pic circuits I play with. It has switch selectable 3, 4.5, 6, 7.5, 9, 12 volts out at one amp. My pic breadboards have on board "whatever to 5 volt" three terminal regulators, along with 3 AA batteries, and a RS232 programming connector along with a solderless breadboard. The on board 5 volt reg is only a 78L05 so it can't put out more than 100 milliamps to power the pic, then I use higher voltage and power supplies for the heavy loads.
On Wed, 08 Aug 2012 09:09:29 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

>On 8/8/12 5:27 AM, Rich Webb wrote: >> On Tue, 07 Aug 2012 17:39:32 -0700, Daniel Pitts >> <newsgroup.nospam@virtualinfinity.net> wrote: >> >>> Is it just me, or is deciding on a power supply a relatively difficult >>> problem, compared to other aspects of working on digital circuitry? >> >> s/deciding on a power supply/analog design/ -- Yes, although it can be a >> lot of fun. >> >> If you don't need portability then krw's suggestion of a regulated wall >> wart is spot on and by far the simplest. Do ensure that the output is >> actually regulated, though; some are not more than a step-down >> transformer with a diode bridge. >> > >Okay, that all sounds good for now, and that's the approach I'll take. >Although, how do I verify if it is actually regulated or not?
Generally (one expects that there may be exceptions) all you would need to do is to check the unloaded terminal voltage. If it's (pulls random wall-wart out of drawer) labeled "output 6 VDC 100 mA" and the no-load voltage is 8 V then it's not really regulated. At its rated load it should drop the extra 2 V internally (i.e., its output impedance is about 20 ohms) so whatever it was intended to be plugged into would get close to 6 V. What else is handy... a "7.5 V 1000 mA" that measures 9.5 V unloaded and a "12 V 400 mA" that's a spanking 18.5 V. There's also a "3.6 V 1 A" that's reading 3.4 V. The last one is noticeably smaller and lighter than the traditional transformer + bridge style. It's probably a tad low since it isn't seeing its recommended minimum load (prob 100 mA or so). A random 7 to 9 V wall wart paired with a simple 7805 linear regulator on your breadboard might be a better start. You'll start to become acquainted with filter caps and (possibly) heat-sinks but also another step towards a DIY project.
>In any case, I would like to know more about how to work on this kind of >thing in the future. For instance, I need to replace my sprinkler >system panel, which uses 24V for the valve controls, but I'll probably >end up using 5V or 3.3V ICs for most of the rest of the circuit. > >Also, some idea's I had for projects require higher voltages. I'd be >interested in creating a Geiger Counter, for instance. I'd also like to >play around with EL wire for a project. Both of those require much >higher voltages. > >Basically, I'm self-taught here, and would like some guidance on how >best to learn when/why to use various methods of power supply, and how >to design/build those.
Wouldn't hurt to pick up a copy of "The Art of Electronics" and its companion workbook but you could start with some of the manufacturer application notes at, say, National and TI (now joined at the hip) or even the Wikipedia entry on voltage regulators. -- Rich Webb Norfolk, VA
On Wednesday, August 8, 2012 2:39:32 AM UTC+2, Daniel Pitts wrote:
> > Now, if I'm reading the specs right, I think I can power the whole thing > on 3 AA batteries (4.5 volts).
The problem with batteries is...they're not 1.5V! They start out at about 1.56V when new, rapidly drop to about 1.3, gradually drop to about 1.1, then rapidly drop to zero. Your 3xAA batteries will start out at 4.6V then drop down to between 3.3-3.9V for the rest of their lifespan. You have to design for that.
> Is it just me, or is deciding on a power > supply a relatively difficult problem, > compared to other aspects of working > on digital circuitry? >
No, it's difficult. An easy way to get 5V is with a wall-wart or USB cable (as you mentioned). If you want batteries it's a bit harder. The ATtiny chips work on a wide range of voltage so they should be OK with 3xAA. The brightness of the LEDs can vary quite a lot though. You can design all sorts of circuits to get around this but it's far, far easier to go to ebay.com and type "5V DC boost". That will get you a little PCB that gives you a constant 5V DC from batteries. I've been using them a lot lately and they're worth every penny for projects like this. Some of them even have USB sockets so you can have the option of either battery or USB power with the same cable.
On Wed, 8 Aug 2012 21:37:14 -0700 (PDT), fungus <tooby@artlum.com> wrote:

>On Wednesday, August 8, 2012 2:39:32 AM UTC+2, Daniel Pitts wrote: >> >> Now, if I'm reading the specs right, I think I can power the whole thing >> on 3 AA batteries (4.5 volts). > >The problem with batteries is...they're >not 1.5V! > >They start out at about 1.56V when new, >rapidly drop to about 1.3, gradually drop >to about 1.1, then rapidly drop to zero. > >Your 3xAA batteries will start out at 4.6V >then drop down to between 3.3-3.9V for >the rest of their lifespan. You have to >design for that. > > >> Is it just me, or is deciding on a power >> supply a relatively difficult problem, >> compared to other aspects of working >> on digital circuitry? >> > >No, it's difficult. > >An easy way to get 5V is with a wall-wart >or USB cable (as you mentioned). > >If you want batteries it's a bit harder. >The ATtiny chips work on a wide range of >voltage so they should be OK with 3xAA. >The brightness of the LEDs can vary quite >a lot though.
Several families of CMOS will work on wide voltage ranges, as well. I like to use these, when possible, because having one P/N simplifies BOMs. Brighness variation can be reduced significantly by driving LEDs with a current source, at the cost of some complexity. I've had to do whenever driving LEDs directly from a battery.
>You can design all sorts of circuits to >get around this but it's far, far easier >to go to ebay.com and type "5V DC boost".
Boost regulators will cost power, twice (higher voltage for the ballast resistor to dump and the inefficiency of the boost regulator). It's better to use a current source, if "constant" brightness is needed.
>That will get you a little PCB that gives >you a constant 5V DC from batteries. I've >been using them a lot lately and they're >worth every penny for projects like this. > >Some of them even have USB sockets so you >can have the option of either battery or >USB power with the same cable.
On Thursday, August 9, 2012 3:19:09 PM UTC+2, k...@att.bizzzzzzzzzzzz wrote:
> > Boost regulators will cost power, twice > (higher voltage for the ballast resistor > to dump and the inefficiency of the boost > regulator).
I've measured them at about 90% efficient on 3x 1.5V batteries.
> It's better to use a current source, > if "constant" brightness is needed. >
I don't think a textbook current driver will really be more efficient than one of those little boards. Plus you more of them if there's multiple LEDs. Having a known, regulated voltage to work with makes life sooo much easier.