You’d imagine they would design these modules to allow you to do standard things like put on 8 AA batteries or something… but you can’t even do that on this…
anyway… how exactly do you power it for your projects?
Yeah I’m not really sure why they went with such a wussy voltage regulator in the MiRF. It would have definitely helped if they would have put one in with a bit higher input voltage capacity. Though if you get particularly froggy, you could try to see if you can find another regulator that matches up pin-for-pin with the one that comes stock and swap them.
I personally use LM317 adjustable voltage regulators. They output cleaner power than your average 78xx voltage regulators and cost practically the same money. Plus they give you the obvious advantage of being adjustable and they only need two resistors to set the output voltage. You can also put way more than 7V into them and not see smoke 
.
I don’t think at this point just just being in the prototyping stage that putting your voltage regulators in series with one another is going to hurt. At least use some capacitors in between the regulators to try to filter out the non-DC stuff and you should be okay.
well the problem is… this is a one shot deal… so i gotta get it right the first time (or mostly right)… i don’t want any part in the system to be in question… so i think i’m just not gonna go with it… i think i’m gonna go with one of the older Mirfs that don’t have a regulator… and just input my own 3.3V reg into it like i was going to orginally… i don’t need too much range… so i think that’s what i’m gonna go… thanks for the help though… i still learned a lot… and perhaps in the futurei will use this module
bleh… i just realized…
if i go with the others… then i have to fine level shifters… i don’t nkow if i have enough space for that… ggggrrrrrr WHY!!!
http://en.wikipedia.org/wiki/Voltage_regulator
the very bottom say’s it’s okay to chain a switching regulator with a linear regulator…
so what’s so wrong about putting to linear regulators together??
what kinds of issues do you get anyway?
this is such a headache man… if i cna solve this power issue… i’d be ready to start really working on this project… (the good thing is. school doesn’t start for another 3 weeks… so i’m really getting a jump start here )
http://www.maxim-ic.com/appnotes.cfm/ap … umber/883/
check out the very bottom of this page…
it’s not exactly what I wish i can do… but it’s similar
I guess what i’m asking is this…
let’s say i just go ahead and power a GPS (the GPS issue presents the same problem as the wireless module) and the wireless modules from this 5V regulator… so long as i put a large cap… and a ceramic cap for HF noise… what is the percent of possibility that i will experience issues??
The project I’m working on right now I’m running 3.3V out of my LPC2148 board straight into the MiRF board. Just hook the regulators in series and it’ll be okay…seriously. I wouldn’t freak out too much.
There are two main issues with hooking two regulators in series with one another. The first is that you get the noise from the first regulator in the second regulator (so you end up with double the noise coming out of the second regulator). The other reason is that you don’t get the full capacity out of both regulators like you would if they were both hooked up in parallel. In your particular case, you would be getting the full capacity out of your 3.3V regulator, but not the 5V regulator. Essentially whatever current that is going through the 3.3V regulator is current that your 5V devices cannot use. You must remember that when you figure out what current capacity you size your 5V regulator.
If I were in your shoes, I would just try to get the best quality regulators I could. No less quality than LM317s - I would definitely stay away from 7805s and 7833s. And be sure to use capacitors and maybe a filter in between them like I’ve mentioned several times.
Thanks for the replies
No problem, man. I hope I was able to help you more than I confused you. 8)
brennen:
No problem, man. I hope I was able to help you more than I confused you. 8)
oh no no no…you definatly helped… at this point i’ve done enough researched… and have figured out how i’m going to approach this project… thansk a lot… i’m at the point where i can start ordering parts and building stuff…
Not to be nosey, but what did you decide to go with?
i went with the mirf V2… the one that takes the RP-Sma antenna
they should be coming in the mail in the next day or two…
Rancid,
If you are worried about running LDOs in series, get this instead:
http://www.sparkfun.com/commerce/produc … cts_id=151
Not only is it $5 more, but has a fantastic range and you can use it in future projects if needed (control a robot maybe :P)…
d’oh, there’s a page 2 hehe…
You should be fine. Just use a nice big cap between the LM317T and the MiRF-v2, say 100uF and you should be ok… configure the vreg as follows:
http://www.uoguelph.ca/~antoon/circ/vps.gif
You should only be looking a the vreg in this circuit, and for your application you can ignore the protection diode. I’m just using this to explain R1/R2 and setting up the 317T. If you already know how to do this, forgive me, just thought it’d help ya! **note: in the circuit, R2 is infact P1… It’s this voltage divider that sets up a Vref, thereby setting the output regulated voltage.
Then you can adjust the 5K pot and set your output. To be safe, you can even calculate the set resistor (the equation is in the datasheet) or just measure the resistance across the pot once set and replace it with a fixed resistor. The datasheet recommends a 240ohm resistor, and with your output of 5vdc, R2 (or P1 in this case) would therefore = 720ohm, so use the NPV 
Considering the complexity of that schematic that bsodmike has shown, here is the picture of the typical circuit from the LM317 datasheet:
http://www.national.com/images/pf/LM317/00906301.jpg
You’ll want to put that big capacitor that both bsodmike and myself have mentioned in parallel with C1 on this schematic. C2 here is shown as a tantalum capacitor, and considering their expense, I would recommend going with a 50 to 100 uF electrolytic in its place (this is mentioned in the datasheet).
D1 in bsodmike’s schematic is optional, but in general doesn’t hurt. Diodes are pretty darned cheap, especially if you order them in a bit of quantity.
For the schematic I’ve shown, the input is expected to be DC, which is how your circuit will work. If you want to give the user the option of putting AC in, then you have to go with something more like bsodmike’s circuit with the full-wave rectifier and the huge smoothing cap (C1 in his schematic). The LED in his circuit is also optional (the LED is L1…the L preface is usually reserved for inductors, but i digress).
I think you’ll be happy with this setup. You can find info on the LM317 at http://www.national.com/pf/LM/LM317.html, and there is a handy website I use for calculating the resistor values at http://www.electronics-lab.com/articles/LM317/ so you don’t have to use a pot if you only want a fixed output voltage. This is cheaper but takes away the flexibility of the voltage adjustability.
a word of caution. you will need a huge heatsink if you are going to run it at lower output V and higher output current. at 5V, 1.5A, your 317 will be dissipating around 37.5 watts (25*1.5). this is pretty huge. a TO220 package will handle up to 1 W in free air.
personally, I’d build 3 or 4 supplies in one: 3.3V, 5V, 12V and 1.5-30V. Use a seperate 6V transformer for the lower supplies and a LDO for 5V. The regulators will still need heat sinks but may actually survive.