Help With Extending Laptop Docking Station's Power Button

JeffesonM · 04-12-2003, 04:27 AM

I'm using an IBM T21 in a docking station for my carPC. Not as cool as an integrated solution, but it will work for the short term.

I'm planning on putting it into a docking station under the passenger seat and I would like to extend the power button on the docking station to somewhere in my center console.

The button on the outside of the docking station:

actually pushes a little button on the inside of the docking station:

I'm a novice when it comes to small electronics, but I know that I'll need to get a switch and solder its leads to some of these pins.

So my questions are...
1. What kind of switch do I need? I know it has two different actions, depending on if you press it once or hold it down for a few seconds.

2. Any idea which pins (1-5) I'll need to connect to? If not, how might I go about testing this?

3. Do I need to de-solder the existing leads, or remove the existing (inner) button?

Thanks for any help anyone can provide.

Alanh · 04-12-2003, 02:12 PM

I don't have an IBM, so I can't comment on that exact unit, but I did something similar to a Dell docking station.

Mine has a switch with two pins that are connected when you press the switch, so I just wired an external switch in parallel. The switch I used is a simple single-pole momentary contact pushbutton switch that is normally open (when you aren't pushing it down). To make it easier to disconnect things, I mounted a small two-wire audio jack on the docking station and wired between the switch pins and the jack. Then I made a cable with my auxiliary switch on one end and a mating plug. That way, the docking station is easier to remove if needed. I mounted the jack to a hole I drilled in the plastic case.

(Be real careful if you start drilling holes, to make sure you don't damage something or drill where your jack won't fit!)

Some general comments...

If you get different action by pressing on the switch for a longer time, that tells me that it must be a momentary contact switch. In other words, the switch contacts change to either opened or closed only when you press on the switch and don't stay in those positions when you take your finger off.

I would think that it probably is a switch that makes contact when pressed instead of the other way around. That is a pretty common way of doing things.

Are you sure all the pins on the switch are actually used? 5 sounds like a lot. Some may only be there for mechanical strength. The following pretty much assumes that only two of the switch pins are actally used...

If you have a multi-meter, you can measure the voltage on the pins and see what readings you get when you are and aren't pushing on it. Look for pins where the voltage readings change from not pushed to pushed. There should be one always at ground or at some voltage too. I'd expect the pin with the changing voltage to have the same voltage as the other pin when the switch is closed. That will give you clues as to what pins are connected when the switch is pushed.

If you have a meter that can measure resistance, you should find that one pair of pins will have high resistance in one switch position and low resistance in the other. I'd probably use the resistance check method first WITH THE POWER OFF! Hopefully, you'll find two pins that have high resistance (open) and then low resistance (closed) when you push the switch. If that is the case, then you get a single-pole momentary contact switch (contacts closed when pressed) and connect one pin of your external switch to each of the pins on the docking station switch you identified above, putting the switches in parallel.

Now, if it isn't a simple switch, then it gets more complicated, and thats beyond the scope of this reply.

mp3hombre · 04-12-2003, 06:08 PM

You'll need 1 normally open momentary switch and 2 resistors. The resistors are necessary to avoid any short should the wires get nicked and touch any metal. Just make sure to place the resistors inside the docking station or as close to the power switch as possible, and don't worry about the added resistance.
Solder the 2 wires to the circuit board as shown in the image below and give it a try. If that doesn't work use the alternate point shown by the dotted line.
Good luck and keep us posted!!

JeffesonM · 04-13-2003, 02:29 AM

Thanks for the very thorough responses, guys. I do have a multi-meter somewhere around here, so I'll dig that out and go to town testing the things you described.

And that is a great idea about using the audio plug... I'll definitely keep that in mind.

mp3hombre... I get a "upload.nowherenews.com is not allowed" message when I try to view that picture. I've seen that a few times browsing the board, what's up with that?

mp3hombre · 04-13-2003, 08:25 AM

I've no idea what that message means, perhaps it's your browser or firewall settings. Maybe someone could help us out here.

jol · 04-13-2003, 09:41 AM

Why use restistors? I'd use isolated cables and be good with that

use this adress
http://upload.nowherenews.com/files/41993286.jpeg

Telek · 04-13-2003, 10:47 AM

The server "upload.nowherenews.com" only allows you to access files posted there if the referrer domain is mp3car.com.

If you are using a proxy, or a strange web browser, or anything else out-of-the-ordinary, then the referrer domain won't match mp3car.com and you won't be able to view the picture.

As for why use resistors, it's better safe than sorry. If your "isolated cable" gets pinched and touches the car chassis you can blow your power switch circuit, preventing you from turning on the docking station ever again. Spending $0.08 for 2 resistors seems like a pretty good insurance deal to me.

mp3hombre · 04-13-2003, 04:38 PM

Quote:

Originally posted by jol
Why use restistors? I'd use isolated cables and be good with that

Like I said:"...to avoid any short should the wires get nicked and touch any metal." I suggested them only as a precaution just in case. But you're right, they're not really needed.

ShinkunoNamida · 04-13-2003, 06:34 PM

if you short the power button it shouldn't really bother the system.. you might not be able too boot up though

I would rig up some sort of connector so you could detatch the switch..

JeffesonM · 04-14-2003, 01:40 AM

Okay I located the multi-meter and set to the little Ω. I don't really know how to use one of these too well, but I'll describe what I tested and what I'm guessing it means:

When the two probes are just sitting there it reads .0L M Ω

When I touch them together it reads 00.0 Ω

When I touch one to #1 on that second picture and the other to #3 on the picture, it reads .0L M Ω

Doing the same thing while pressing the button, it reads 00.0 Ω

Is it safe to assume then that these two are the pins I'm looking for?

Also, can anyone point me in the direction of a good internet source for learning about basic circuts?

Telek · 04-14-2003, 02:13 AM

You are correct in your assumptions, easiest way to test it (if you feel comfortable with doing is) is set it up with the case off, and then use a short jumper wire to short terminals 1 and 3 on the switch, and see if it turns on.

If it does then you're good to go.

I just say this because it's possible (however unlikely from the picture) that there are more than 2 pins shorted when the button is depressed, so it could use any pair of pins that are shorted when the button is pushed.

Also (with the power off) check to see the resistance between both of those pins (with the button not pressed) and a ground terminal. If one of the two reads 0 ohms resistance, then you don't need to use a resistor on that wire. If neither terminal (with the button not pressed) reads 0 ohms to ground (i.e. both real .0L Mohm) then you'll need to put a resistor on both.

If you don't want to play with the power on, then solder it up with the resistors and run the wire externally, and momentarily cross the ends of the wire together to see if it'll turn on.

Good luck!

As for electronics help, I don't know of any specific site, but I know that HowStuffWorks is a great generic site for just about anything, and I'm sure that a search on google for "basic electronics tutorial" or some derivative of that will yield a lot of results.

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