DIY: Simple PSP-GPS hookup

**vibez** · August 29th, 2006, 11:29

The fromula I was using is

R=V/I

Resistance(R)= Voltage (V) / Current (I)

I thought (R) was the voltage drop. 3 volts down to 2.5v = 0.5voltage drop.

Where did you get the 500mA value from?

**vibez** · August 29th, 2006, 11:44

Here is the formula I used

http://led.linear1.org/1led.wiz?VS=3;VF=2.5;ID=500

It shows I need a 1/2W or greater 1 ohm resistor

**fokia** · August 29th, 2006, 11:53

Originally Posted by vibez

The fromula I was using is

R=V/I

Resistance(R)= Voltage (V) / Current (I)

I thought (R) was the voltage drop. 3 volts down to 2.5v = 0.5voltage drop.

Where did you get the 500mA value from?

No, R is the resistor value in Ohm...

500mA was a guess, for demo pourpose only... don't know that for sure... probably is a bit high and thus less conservative. I may have to advise you to go for a lower one: 200 or 250mA giving a resitor of ~1KOhm

Tried to check that in ps2dev but the site is down...

P.S.: That formula is known as Ohm's Law

**Rengoku** · August 30th, 2006, 16:37

Hi guys, I got my gpslim236 receiver today, and I've had trouble getting it to work. I made the cable as directed and have tested it with a multimeter. When I use the green screen app, I can see NMEA sentences popping up every second or so, but the Longitude and Latitude values (among others) aren't showing up.

I tried measuring the voltage between pin1 and pin3 on the gps device, and it says its 3V. But when I hook up the cable (with the 1k resistor) and measure it, the voltage stays the same. Could that be the problem? Isn't the voltage supposed to drop because of the resistor?

Thanks
Sorry, newbie here :P

**fokia** · August 30th, 2006, 17:23

Originally Posted by Rengoku

Hi guys, I got my gpslim236 receiver today, and I've had trouble getting it to work. I made the cable as directed and have tested it with a multimeter. When I use the green screen app, I can see NMEA sentences popping up every second or so, but the Longitude and Latitude values (among others) aren't showing up.

I tried measuring the voltage between pin1 and pin3 on the gps device, and it says its 3V. But when I hook up the cable (with the 1k resistor) and measure it, the voltage stays the same. Could that be the problem? Isn't the voltage supposed to drop because of the resistor?

Thanks
Sorry, newbie here :P

Don't seem to have a problem... use the latest MapThis and test you new cable with it. It shouldn't be a major problem deal with 3v for the PSP...

**fokia** · August 30th, 2006, 18:02

Originally Posted by vibez

Here is the formula I used

http://led.linear1.org/1led.wiz?VS=3;VF=2.5;ID=500

It shows I need a 1/2W or greater 1 ohm resistor

You can use that... keep in mind that power dissipation only depends on input voltage.

If it doesn't work try 500Ohm.

**Rengoku** · August 30th, 2006, 18:08

Originally Posted by fokia

Don't seem to have a problem... use the latest MapThis and test you new cable with it. It shouldn't be a major problem deal with 3v for the PSP...

Still no luck

I tried it with the latest MapThis, and it says it's out of range and Data:Bad.

**deniska** · August 30th, 2006, 18:12

Originally Posted by Rengoku

Hi guys, I got my gpslim236 receiver today, and I've had trouble getting it to work. I made the cable as directed and have tested it with a multimeter. When I use the green screen app, I can see NMEA sentences popping up every second or so, but the Longitude and Latitude values (among others) aren't showing up.

I tried measuring the voltage between pin1 and pin3 on the gps device, and it says its 3V. But when I hook up the cable (with the 1k resistor) and measure it, the voltage stays the same. Could that be the problem? Isn't the voltage supposed to drop because of the resistor?

Thanks
Sorry, newbie here :P

Keep in mind that your multimeter would probably display just an average voltage for that AC current...
The danger comes from peaks that could be higher than 3V...
The multimeter would not show the peak voltage, because it's not just fast enough for the transmission frequency... for that reason you probably wont see the drop on your resistor, but your PSP just might feel it...