Hacking the T5000 mobile computer

I purchased a couple of surplus Itronix T5000 mobile computers from Resources Unlimited.  Here is a short feature list, if you haven't seen their ads in Nuts & Volts magazine:

It took me about 12 hours and $20 extra in parts, but I now have my T5000 running my house using an X10 Firecracker wireless interface.  I gotta say, "This thing rocks!"  The T5000 was built by Itronix for Lucent Technologies, and this is one of the most rugged, best built computer items I've ever seen.  I paid $39 for my unit, and consider it some of the best money spent on any surplus item yet.


This is pretty much how I got my T5000 working, and I'm offering this info for general guidance.  I make no claim that this will work for every case.  I could easily have missed something important that will eventually damage a unit (even mine) modified this way.  You are on your own, and I take no responsibility for any damage done to your unit based on these instructions.

To hack this machine, you will need to buy or build:

You will also need access to another PC of some kind running a version of DOS, usually not a problem for anyone reading these pages.

The 8.8 VDC power supply

This is the power supply that will run the T5000 and recharge the NiCd battery pack.  RU warns that this supply must not exceed 10.5 VDC, or you risk damaging the unit!  So I was very careful in my construction to stay within this range.

The simplest way to build this supply is head to Radio Shack and pick up

Build up an adjustable power supply using the LM317, trimpot, resistor, one diode, and caps.  The schematic for this supply is widely available; you can even find a copy of it in my book, Build Your Own Robot!, where it appears as a gel-cell battery charger.  If I don't get around to including a schematic here, visit the National Semiconductor web site and look for a LM317 app not.  I didn't even use a perfboard for this; just wired it free-form in kind of a lump.  Pay attention to polarity on the LM317 , the diode, and the caps.

Wire the anode of the last diode to the positive output of this power supply.  The cathode of this diode becomes the power supply output lead when you wire the supply to the T5000.

Drill a 1/8" hole in each end of the project box.  Cut the plug off of the adapter cable and discard it.  Cut the white cord on the 9 VDC power supply wherever you want to insert the LM317 regulator you just built; I cut mine about one foot from the plug end of the cable.  Thread the two free ends of the wire through the holes in the box.  Wire the end from the power supply output to the input points on your LM317 supply.  Use a voltmeter to make sure you wire the correct lead to ground!  Hook the remaining length of cable to the output points on your LM317 supply.

Plug the 9 VDC power adapter into the wall, then adjust the trimpot on your LM317 supply to get 8.8 VDC output. Strip insulation from the free end of the output cable, then tin the ends with solder.  Use a voltmeter to verify which lead is positive and mark that lead.

Put the lid on your project box.  The 8.8 VDC supply is done!  In the next section, I'll describe how to hook the supply to your T5000.

The 7.2 VDC NiCd battery pack

The T5000 as shipped is missing its 7.2 VDC battery pack.  This is the power supply used if you want to run the unit in the field.  It is also the only source of voltage to maintain the clock and the A: RAM drive.  Like it or not, you need to supply this voltage if you want to get any real use out of your T5000.  You have two options here, based on your intended use.

If you want to use the T5000 in the field, you need to track down a large 7.2 VDC NiCd pack that fits the case.  Note that the T5000 has a three-pin connector for the battery: Gnd, 7.2 VDC, and some type of temperature sensor.  I have no details on the temperature sensor used.  If you go this route, you will need to construct a power supply that plugs into the mains input on the back of the T5000.  This is the round hole with the pin in the center.  I have no info on building such a supply beyond that offered in the Resources Unlimited docs.

If you only intend to use the T5000 in the home, running it solely off the power supply above, you can use just about any little 7.2 VDC NiCd pack.  I used a pair of Radio Shack 3.6 VDC 300 mAH cordless telephone batteries (23-280).  Note that these are discontinued, and I was able to pick them up on clearance for less than $2 each.  The rest of these instructions assume you are using the small battery pack, and will run your T5000 off of the power supply just constructed.

If you opt for the two 3.6 VDC batteries, wire them in series to get a 7.2 VDC battery pack.  Prepare a 3-pin female socket that fits the T5000 battery connector.  Wire the socket as follows; this assumes you are viewing the T5000 from the underside, with the handle on the left and the labels inside the battery compartment oriented properly for reading:

Finally, connect the negative lead of the NiCd pack to the negative lead of the power supply.  Connect the positive lead of the NiCd pack to one end of a 470 ohm, 1/4-watt resistor.  Connect the other end of the resistor to the positive side of the power supply.  This resistor limits the amount of charging current into the battery pack to about C/20, or 300 mA / 20, or 15 mA.

With both power supplies built, you are now ready to power up the T5000...

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