Electronics nerds?

[Disco Dan]

I have a big pile of resistors, now I can identify each one (big range of values) but which one would I use to change voltage from 10v (sometimes 11v) down to 5v ?

Any help would be much appreciated!!

What I have got going on here is making a charger for my satnav - I have found a cell phone car charger and cut the end off. The two wires are putting out 10v and i need to put a mini USB plug on the end which should have only 5v going into the device. (it is already stepping the voltage down from 12v to 10v inside the charger unit)

[The Pastor]

voltage = resistance x current.

What you want is a voltage divider

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

[Disco Dan]

I have some bread-board lying around if a simple circuit is required rather than just an inline resister.

[avgas]

ok without the super detail, do you need a specified current?
I have attached a basic drawings.
To half the voltage you need 2 of the same resistor (R) and a cap (220uF?) and a 5V (or 5.1 i think it is) Zenner diode.
The rail along the bottom is ground, top is 10v.
Clear as mud?

[Disco Dan]

voltage = resistance x current.

What you want is a voltage divider

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

um ok

so i have two wires - red and black. They read 10v on multimeter.

So do I need to measure the resistance using these two wires? Because all I get on the screen is "1" regardless of what ohm setting i click it too?

[Disco Dan]

ok without the super detail, do you need a specified current?
I have attached a basic drawings.
To half the voltage you need 2 of the same resistor (R) and a cap (220uF?) and a 5V (or 5.1 i think it is) Zenner diode.
The rail along the bottom is ground, top is 10v.
Clear as mud?

I only have resistors and a few assorted salvaged capacitors.

Any way to do it without a diode?

[Disco Dan]

Oh and I found a few tiny transistors too if that helps?

Tried putting a few resistors inline but it is not changing the voltage :(

I obviously did not pay enough attention in electronics at high school!

[Disco Dan]

Yikes...

Practical Voltage Division
Don't fall prey to the temptation to use a voltage divider instead of a voltage regulator. Voltage dividers are totally dependent on their supply voltage, so don't try to "regulate" 12V to 5 with a divider. However, there are cases where you might want to use a divider. For example, perhaps you have a 5V A/D converter, but you need to measure 0-10V with it. Of course, you will lose precision, but maybe that's OK.
Converting 10V to 5V is easy, right? Two 10K resistors and you have a 50% voltage divider. Except it isn't that simple. If you build a voltage divider in the lab, you'll look at the output with a voltmeter or a scope. All modern DVMs have input impedances of 10M or more, so for practical purposes it isn't there as far as the circuit is concerned. But when you draw real power from the center node, you are effectively putting another resistor in parallel with R2. This changes the circuit and the output voltage.
Suppose your A/D convert has an input resistance of 25K. Now you don't have two 10K resistors. You have R1=10K and R2=10K and 25K in parallel. Resistors in parallel add their admittance, so:
Rtotal = 1/(1/R1+1/R2+.....1/Rn)
If you only have two resistors, this can be simplified to: Rtotal = R1*R2/(R1+R2). So in the above example R2 is effectively 7143 ohms. The divider's ratio is then about 42% (7143/17143). Not the 50% you were looking for. This even happens with a meter, but the effect is so small you don't care. Consider if R2 was equal to 10K and 10M in parallel. That's 9990 ohms and the ratio is 49.97% -- hardly any difference at all, and probably less error than the 5% or 10% resistors you are using.
So when calculating your A/D converter input divider, you want to make R2's total value 10K. If the input resistance is 25K, you have to solve for the parallel resistor with 25K that gives you 10K. So:
10K = 25K*Rx/(25K+Rx)
A little algebra results in:
250K/15K = Rx or Rx=16.667K (you can verify that by computing 16.667K in parallel with 25K).
So the actual voltage divider would be R1=10K, R2=16.7K, but you can't really find that value more than likely. Substitute a 15K resistor and you'll find the true division ratio is just over 48% (can you get the same result?). However, 16K is a standard value and provides a ratio of 49.4% which is pretty close.

[Mikkel]

Just grab a green one... Green is good! Green will do the trick :yes:

[Hitcher]

Go to Duck Smuth and buy one of their $20 cigarette lighter-USB adaptors. Then buy an extension cord with a USB plug one end and a USB-B five-pin plug on the other. Connect it all up, and Bob's your father.

I have done this, and it works.

[Ixion]

'Taint simple. Mainly cos your car charger is outputting DC. If it was AC it would be much easier you could just take the 0 to 5v + a bit part of the AC curve and regulate and smooth it.

I looked at EXACTLY the same issue for my Navman. WTF Navman don't provide a hard wire cable GOK. You can buy them in the UK but they are a horrendous price.

So, what I did, I popped into Surplustronics at the top of Queer St, and bought a little unit that does exactly that - converts 12v to 5v . Hard wire it in, sod the silly cigarette lighter thingie. About $30 ish. About the size of a match box. Explain what you need to the dude, they are on the rigjht hand wall as you enter the shop, sort of behind the counter.

I'll look and see if mine has a name on it.

[avgas]

Ok will clear this all up after work, a few misconceptions here - but am flat stick right now.
yes you can do this setup without the diode, and no AC does not affect the design i did before. Yes it is better to use a regulator (LM, 5V range - LM3501? Sorry its been a while)

[CookMySock]

I have a big pile of resistors, now I can identify each one (big range of values) but which one would I use to change voltage from 10v (sometimes 11v) down to 5v ? Thats not a smart way to do that.

go here http://search.dse.co.nz/ and search for "7805"

The LM7805 is a 5V regulator. It costs $1.50

Scroll down abit theres a link called "A Typical 78xx Power Supply Circuit". You only need the two capacitors to make it work.

Trim all the wires really short and solder it together xmas-tree sylez and pot it in some epoxy inside a matchbox or smaller.

Easy. Fast. Reliable. Cheap.

DB

[Disco Dan]

The OEM Navman charger is available at DSE for $49.

The idea is to do this as cheaply and simply as possible.


Go to Duck Smuth and buy one of their $20 cigarette lighter-USB adaptors. Then buy an extension cord with a USB plug one end and a USB-B five-pin plug on the other. Connect it all up, and Bob's your father.

I have done this, and it works.

Will go and check it out - I have already wired up a cig lighter socket under the seat (so i can also charge my phone).


'Taint simple. Mainly cos your car charger is outputting DC. If it was AC it would be much easier you could just take the 0 to 5v + a bit part of the AC curve and regulate and smooth it.

I looked at EXACTLY the same issue for my Navman. WTF Navman don't provide a hard wire cable GOK. You can buy them in the UK but they are a horrendous price.

So, what I did, I popped into Surplustronics at the top of Queer St, and bought a little unit that does exactly that - converts 12v to 5v . Hard wire it in, sod the silly cigarette lighter thingie. About $30 ish. About the size of a match box. Explain what you need to the dude, they are on the rigjht hand wall as you enter the shop, sort of behind the counter.

I'll look and see if mine has a name on it.

Will have to remember that! Cheers

[dhunt]

I have a big pile of resistors, now I can identify each one (big range of values) but which one would I use to change voltage from 10v (sometimes 11v) down to 5v ?

Any help would be much appreciated!!

What I have got going on here is making a charger for my satnav - I have found a cell phone car charger and cut the end off. The two wires are putting out 10v and i need to put a mini USB plug on the end which should have only 5v going into the device. (it is already stepping the voltage down from 12v to 10v inside the charger unit)
For what you want it for I would say a resistor divider is not suitable at all for what you want.
What you want to do is got to DSE and buy a LM7805 (5V voltage regular) and a couple 100n ceramic capacitors and make a properly voltage regulator. Depending on current consumption and voltage input you may need to use a heat sink (Piece of Metal). If you need more details let me know.

[Disco Dan]

ok, cheers for all your help folks... going to head down to DSE glenfield and check out what they can do for me.

Either voltage reg or cig lighter adaptors.

[nodrog]

make sure you take a fire extinguisher with you when you test it out :sunny:

[Disco Dan]

Ok, just went and got myself one of these:

http://www.dse.co.nz/cgi-bin/dse.storefront/482a4d9701f913402741c0a87f3b0692/Product/View/M9944

but bugger me if i ran into another problem!

...you see when I connect a mini usb plug to Navman it thinks it's connected to a computer and turns itself off!

So now I am hoping that if i cut the usb-usb mini cable and cut the data wires then re-attach just the two power wires it should charge while still being 'on'.

If not.. then I will have no choice but to buy the OEM charger... grrr :argh:

[dhunt]

Ok, just went and got myself one of these:

http://www.dse.co.nz/cgi-bin/dse.storefront/482a4d9701f913402741c0a87f3b0692/Product/View/M9944

but bugger me if i ran into another problem!

...you see when I connect a mini usb plug to Navman it thinks it's connected to a computer and turns itself off!

So now I am hoping that if i cut the usb-usb mini cable and cut the data wires then re-attach just the two power wires it should charge while still being 'on'.

If not.. then I will have no choice but to buy the OEM charger... grrr :argh:
I would actually assume the the data wires in the power supply you just got are not connected anyway.

Does the OEM Navman charger use the usb port to charge the unit?

[Disco Dan]

I would actually assume the the data wires in the power supply you just got are not connected anyway.

Does the OEM Navman charger use the usb port to charge the unit?

Still thinks it's connected to a computer!!!! :argh:

only port is a mini usb socket on the bottom - connects to a pc

The charger also uses this socket.

It's still turning off when i connect it with only the two wires :( :( :(

[Disco Dan]

How on earth can it tell the difference???

Unless - it DOES use the data wires - ie oem charger supplies small voltage through data wires?

But then again, a computer would send a signal through the data wires!!

[vindy500]

suck it up and buy the oem charger, you dont want to lose your warranty

[dhunt]

1) What is the normal behaviour when you plug it into the a computer? Does it turn off then?

2) After it has turned off (while still plugged into your power supply) can you turn it on?

[Disco Dan]

suck it up and buy the oem charger, you dont want to lose your warranty

well if you can imagine that when my bike got stolen the mounting bracket and charger were on the bike...

They are $49 each

Last week I bit the bullet and bought a RAM mount for $140

That blew my budget and thus I need a cheap/free solution to charge it.

I have already bought a cig lighter socket for about $6 and now a usb cig socket for $25.

I was REALLY hoping I was not going to need to buy anything else.. let alone having to pay $49 for the oem charger! ! !

[Disco Dan]

1) What is the normal behaviour when you plug it into the a computer? Does it turn off then?

2) After it has turned off (while still plugged into your power supply) can you turn it on?

When plugged into computer via USB it turns off and displays a graphical image showing it is connected to computer via usb.

When plugged into my power supply on the bike it does the same thing. Pressing the button does nothing.

Could it be related to the full size usb socket on the other end (connected to the new adaptor i just got) ? But then again with the data wires cut it may as well not be there anyway since it's only supplying power!
]

Just does not make any sense!

[Disco Dan]

I am pretty sure the oem charger only has two pins inside the mini usb plug (that goes into navman) though?

But I doubt if it is possible to disasemble the plug and remove the extra pins.

Could it be detecting the pins?

I think I will attempt to lever out the pins with a knife and see if it makes any difference. Cut the cable to bits so got nothing to lose now!

[dhunt]

How do you normally charge it? Through the computer? If it's a wall pack what is the output voltage?

[Disco Dan]

How do you normally charge it? Through the computer? If it's a wall pack what is the output voltage?

i normally charged it while it was on the bike using the car charger.

Since the charger was stolen I have used a usb cable from my computer to charge it.

Does not use a wall pack to charge.

I have just snapped off the middle pins on the mini usb plug, leaving only the two power pins and tried that - no change.

Really got me stumped.

Not sure what to try next.

[Disco Dan]

1) ruled out 'data pins' being detected - both cutting the wires and removing the pins in the socket.

2) could be a voltage difference - but USB is pretty standard at 5v

3) Could be the 5th pin - which as you can see in diagram above is not used. Maybe Navman uses it to tell between the charger/pc. If that is the case.. i've already removed it. even if it was there, there is no wire and the plug would have to be butchered beyond usable to try applying a voltage.

[Disco Dan]

Ok found a bit more info...

Looks like the 5th pin DOES do something... but it says "type B - pin 4 not used".

"pin 4 - Permits distinction of micro-A and micro-B plug. Type A plug - ground. Type B - not used.

[Disco Dan]

Also.. according to the uk forums on these other people have had this problem - buying 3rd party chargers.

Various people suggested removing the middle pins and/or cutting the data wires. But no-one seems to have managed to get it going yet!

[Disco Dan]

This is so frustrating, as the built in battery is next to useless... I went from glenfield to barrys point road and back and it was almost flat!

I am going to be seriously peed off if I have to buy the oem charger after all this kurfufle

[Disco Dan]

Think i'm gunna kill.... :argh:

just found this... (pic)

Seems the stupid twat that originally quoted me $49 for the charger was wrong...

OMFG

Right. tomorrow I am taking the usb thing back and getting the oem charger. Bastards.

Navman 1
Disco 0

This is not over navman!!!!!! :angry2:

[avgas]

Disco drop me a PM and i can pass you the email of a good friend of mine who designed alot of the Navman ICN and marine stuff. He can tell you what the story is.
Generally mini usb just charges off the supply pins. However i have had a device that received a 'charging' message from the comms pins too. Pissed me right off.
On the other side if you wanted to be green you could use this (http://www.trademe.co.nz/Electronics-photography/Other-electronics/Adaptors-chargers/auction-155185979.htm)

[xwhatsit]

Disco, that thing where it thinks it's connected to a computer sounds familiar. I build an iPot charger (well, any USB charger), and the interesting thing about charging an iPod, is that it gets the voltage from the power pins on USB like normal. However, it won't actually charge until you trick it into thinking it is connected to something; the way you do this is put a small resistor between the data lines.

This method of detecting connection seems common across many devices that charge via USB. You probably have to find the resistance value the Navman is looking for. Maybe it's nothing and you have continuity between the two data pins?

[imdying]

$35 for the oem one ehh... you've spent more than 3.5 hours on this judging by teh time stamps... your time has gotta be worth more than $10 an hour surely?

[xwhatsit]

$35 for the oem one ehh... you've spent more than 3.5 hours on this judging by teh time stamps... your time has gotta be worth more than $10 an hour surely?

You should know better than this -- you're missing the point :innocent:

[imdying]

You should know better than this -- you're missing the point :innocent:Heh, yeah I know... but I did learn a while ago, there's not much point making anything you can beg/borrow/steal/buy :)

[Disco Dan]

Got my money back on the USB thingy, now have to wait while they order the oem charger... :angry2:

[Disco Dan]

Grrr... anyone notice my new problem? :angry2:

[vindy500]

wrong usb plug?

[imdying]

Some days you just want to curl in a ball and die :(

Hack saw time :D (I assume the mount is blocking the right angle plug body?)

[Hitcher]

Ahh. The dreaded primary interface problem.

[Disco Dan]

Some days you just want to curl in a ball and die :(

Hack saw time :D (I assume the mount is blocking the right angle plug body?)


Ahh. The dreaded primary interface problem.

yes, and yes.

Looks like I will have to get out my hacksaw and start cutting the overly expensive-I-moaned-about-it-for-ages-mount just to make it fit... *sigh*

I'm betting after all this kurfuffle the bloody navman will shit it'self and i'll have to start all over again... :crybaby: