gps module & BS2 & high voltage smell?

theloneduck

Hi all,
I was fortunate enough for Santa to bring me·the·GPS module for Christmas.· When I plugged it in and went to test it with my bread board and bs2 using the documentation code and diagram, it was blinking red (as expected) but it started to give off a funny smell (you know the burning electronics smell).· I unplugged the 9volt from the BS2 board but I heard a pop before I could get it removed.

I later went and checked the voltage and it was giving a 4.93 as the voltage from my multimeter which is in the operating range for the voltage (Vdd to Vss)

Does anyone else get this smell or is it something wrong in what I did to hook it up?
-TLD

Franklin

You don't say how you hooked it up but a smell is not normal.

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- Stephen

theloneduck

I hooked it up like in the DOCs (page 2 of http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/GPSManualV1.1.pdf·) or see jpg attachment.
The code I ran was the DOC code as well (see the .BS2 attachment)

PJAllen

Which "board" are you using the GPS with (BoE, HomeWork, PDB)?

theloneduck

It is the one from '123 robotic experiments for the evil genius'

Post Edited (theloneduck) : 12/29/2007 4:18:10 PM GMT

PJAllen

OK, so the board is one that you've made.·

Sorry, but I don't have that book, but perhaps you could scan the page and U/L it.·

[noparse][[/noparse]Check your wiring, OM.]

theloneduck

Here is the schematic I was using.· Sorry for the tilt on the board.

The resistors are 220 Ohms

PJAllen

OK, here's what.

The GPS needs 115mA and that's more than the BS2's on-board regulator (the source of your "Vdd" /·5V)·can deliver.

I cannot say how the on-board regulator would fail in such an over-current event.· It's likely the source of the "pop" and the burny smell you've noted.· Better assess the situation without the GPS connected.· Does your BS2 still program, operate, etc. without the GPS connected?

Given your set-up, the·GPS needs its own 5V supply.

theloneduck

forgive me as Im a newbie to electronics...

so the GPS module is trying to pull too much current from the stamp?· The code still runs fine when I run it without the GPS module (except the part about retreiving data from the module).

·

Mike Green

The on-module voltage regulator will shut itself down to protect itself. PJ Allen is correct that you can't power the GPS unit from the Stamp's regulator. That doesn't explain the pop and the smell though.

theloneduck

So i guess 2 questions...

1) how much amperage does the BS2 push out via VDD

2) where does one find a 4.5 - 5.5 Volt battery?

PJAllen

1. I believe that on-board regulator is good for around 50mA.
2. Three AAA, AA, or C, or D (@ 1.5V) cells in series = 4.5V

Mike Green

The BS2's regulator is also used to supply the BS2 and the other circuitry on the module, so there's not quite 50mA available. Figure maybe 30-40mA.

As PJ Allen mentioned, you can put 3 alkaline cells in series, but the voltage is likely to stay in the 4.5 to 5.5 V range for only a short time. The battery's output voltage shifts with the load on them and decreases as they're drained of energy. You really need to have a voltage regulator and feed it with a higher voltage. Typically you use a "low drop-out" regulator that only requires an input voltage about 1/2V above the output voltage. For a 5V output, this is usually a 6V input supply, typically from 4 alkaline cells or 5 NiMH rechargable cells. You can also use an older / cheaper regulator ... the LM7805. This requires a 2V difference between input and output, so you'd run it from a 7.5 to 9V unregulated supply ... typically 5 alkaline cells or 6 NiMH cells.

Parallax's development boards' schematics are downloadable with their links on the webstore pages for the product. Download one of them (like the Board of Education) and see what they've done for their 5V regulated supply.

PJAllen

Thanks for going those extra miles, Mike Green.· There's been a lot of onion peeling in just getting to this point.· I wondered that I'd be presenting too much information and decided to just let things take (or continue on) a more organic [noparse][[/noparse]?] course.


Post Edited (PJ Allen) : 12/30/2007 3:42:18 PM GMT

Forrest

Since your using a GPS - you may want to check into a RC battery back such as one of these www.radioshack.com/family/index.jsp?categoryId=2818347&cp=2032056.2818124 feeding a +5V DC power supply circuit www.tkk.fi/Misc/Electronics/circuits/psu_5v.html. All the parts are available at Radio Shack.

sdy

Lone Duck, Use what Mike said, an LM7805. See it here, http://www.fairchildsemi.com/ds/LM/LM7805.pdf
Connect it like Fig 7. Use 9 V connected to pin 1, the Input.
You can get it RadioShack:
http://www.radioshack.com/product/index.jsp?productId=2062599&cp=&sr=1&origkw=regulator&kw=regulator&parentPage=search

theloneduck

Thanks to all who helped out.·
just a point of clarification for me... it I run a 9volt through the 78L05 to regulate the voltage to 5 Volts, do i need a resistor to pull the amperage down to 115mA?· And (according to some quick v/i=r calculations) it would be about 43 ohms correct?

Sorry for all the questions, like I said, Im rather new at this.

Mike Green

The regulator supplies the resistance needed to reduce the voltage available regardless of the amount of current drawn (up to the maximum supported by the regulator and with respect for the amount of heat generated). That's the whole idea of the regulator. A GPS receiver actually draws a variable amount of current depending on what it's doing at the moment. The regulator adjusts for this as needed so the voltage available remains the same (5V).

PJAllen

You will have to get a 7805, a 78L05 is only good for 100mA.

sdy

No resistor needed.

allanlane5

I'm pretty sure a 9-volt "transistor" battery won't supply 100 mA for very long, and probably won't supply 100 mA at 9 volts at all. For that level of current, 4x 1.5 volt alkaline AA batteries (and maybe 6x 1.5 volt batteries, if you MUST have 9 volts) will be needed.

You really need to read the manual for the GPS module as to what voltage it expects. It sounds like it expected 5 volts, you supplied 9 volts, and the "pop" and smell was something being cooked to death. But maybe you're lucky and did no permanent damage.

Note, on the BS2 BOE board, they use a 7805 "TO220" package, which will regulate up to an amp of current at 5 volts output. I wouldn't use the regulator on the BS2 itself to drive ANY external circuitry myself.

theloneduck

Thanks to all who helped.. I got it working..

The module and BS2 work fine now I have the last 7805 Radio shack had in stock.

If anyone is interested, attached is the debug window.