Sourcing and assembling my test rig

[sry_not4sale]

OK... whats a caps? capacitor?

[sry_not4sale]

http://jaycar.co.nz/productView.asp?ID= ... rm=KEYWORD

^ Would one of these regs be OK?

[jharvey]

Yes caps means capacitor, with an implication that it will require a couple capacitors. A big electrolytic, is nice because it stores enough energy to get over small supply blips. Small ceramic caps are nice because they have lower internal resistances that allow them to react very quickly. A rising edge of the CPU clock will draw very large current spikes, for very short periods of time. The internal resistance of the large cap can't provide the required current spike, so you end up with a low voltage issue, or at least for a couple nano seconds.

For more info, see the power reg page of freeems 1.0's schematic. There is a descriptive block there that helps break it down some. You can probably get by with just two caps.

[jharvey]

The 7812 requires at least 14V in to provide 12V out. I believe the TA card works off 5V so you want a 7805, which will require an input of at least 7VDC. If you supply a 7805 with say 5.5V the output will be closer to 4V not 5V. From 1.0, I see these parts that will likely get you close to what you need. Buy some extras, they aren't very expensive, and are very handy for other projects as well.

2200uF,newark,69K8230
.1uF,newark,56K3664
7805,newark,45J1442

The 2200 uF might be a bit large for bread boarding. Might want to check the physical size of that fellow. Also you really want a cap on the input, and on the output. If not these regulators like to oscillate.

[Fred]

Mate, skip the 7805 and go straight for an LDO 5v reg. Any LDO 5v reg with 500mA or more is OK. It should have 30v input or more max rating too. If you do this, you can use it on the car too.

Caps, yeah, Jared covered it pretty well.

Fred.

[jharvey]

I think I'd agree with that. I believe Low Drop Out regulators have a couple mild gotchas, but shouldn't be that big of a deal. I found this one, it looks like a near direct match to the 7805.

Newark LM2940CT-5.0

Basically it's the same thing, cost's like $.40 more, however it can make 5V with an input of 5.5V, where the 7805 requires 7V in, to make 5V out. I seem to recall the LDO's are more sensitive to things like ESD, and the more sensitive internals are less friendly if you rely on the over temperature protection, over current protection, ect.

For example, if you overload the 7805 with a near short circuit, and no heat sink, it will typically back itself down quick enough to prevent damage. However, the LDO's are more likely to become damaged, as the thermal overload has to be more picky about backing the temperature down. The real solution in both cases, is to give it a proper heat sink (assuming the package allows a heat sink that is), or don't short the output. Some times on a bread board, you don't bother to add the heat sink as it's not required for your normal 25mA draw. Then you put a wire in the wrong hole, or you have a small solder bridge, and poof.

In your case I understand you are working with a 12V supply, so you are well above the 7V required by the 7805. You're also less experienced with the electrical side, so I suggested the 7805 because it's a bit more rugged. Both chips are fine candidates.

If you had a 6V supply then you would certainly want the LDO. One of the most common places for LDO's are devices that are powered by 4 batteries and requiring 5V. These LDO's are handy for keeping the wasted heat down, well allowing for a 6V supply.

[jbelanger]

I think you'll burn traces before you fry an LM2940 (or LM2937) if you short the 5V output. They will just shut down if they get too hot. They are well suited for this application.

Jean

[jharvey]

Newarks, 41K4548 for the LM2937ET-10/NOPB cost about $2 in qty 1. I buggered the above about the LM2940, it requires quantity to get it for $.80, this one is the same thing, but cost $1.75 in qty 1 Newarks 41K4577. The LDO's cost a bit more.

The 7805 is $.50 in qty 1.

[sry_not4sale]

Jaycar in NZ:

http://jaycar.co.nz/productView.asp?ID= ... BCATID=320
LM2940CT-5 5V 1A Low Voltage Dropout Regulator
$9.90

or

http://jaycar.co.nz/productView.asp?ID= ... BCATID=320
7805 +5V 1A Voltage Regulator
$1.90

[Fred]

Aaron, 2940 is what runs my ute and my freeems setup. If you plan to actually use this, get it. If it's purely for the bench, 7805 is fine.

Fred.