Tag Archives | IpAQ

Ipaq Auto-wake for in-car Applications

updateAs described a couple of posts ago I have set up an Ipaq 2210 in my car for the purpose of GPS navigation; it’s been working very well for a few months now but something stated to bug me; every time I got in the car I had to manually power on the Ipaq. I know it seems trivial and lazy but I just think such a device should be considered part of the car’s instrumentation, it should just sit there doing its thing; you wouldn’t want to have to manually turn on your speedo, rev counter or heat gauge would you?

After much digging I found that the Ipaq (the 2210 at least) could be woken up by applying 5volts to the DCD pin (pin 6) on the base connector; supposedly through a 4k7 resistor although that didn’t work for me so I just fed the 5v straight in (so far so good!). Since my power supply only applies power to the Ipaq at ignition I was able to just take a wire from the power-in on the Ipaq connector across to pin 6 (DCD). Now at ignition the Ipaq gets its 5volts for charging and the DCD gets 5volts to wake it up. There is just one problem; well two actually! The first is simple to fix; when the Ipaq is woken by DCD it tries to sync so the GPS application loses focus. There is an option somewhere in control panel to prevent this behaviour. The second problem is not quite so straight forward. When you turn the key in the ignition you get power for a second (DCD wake-up is triggered) then power is cut for a few seconds while the engine is cranking. Apparently the Ipaq won’t wake up in these conditions! So for this to work you need to turn the car on, wait for the Ipaq to wake up then start the car. Hardly seamless!

In the end I decided to rebuild the power supply with a 10 second delay on the output to the Ipaq. Thanks to Bill Bowden for his Power-On Time Delay Relay schematic.

If you want any more details or the PCB design in either PDF or eagle just let me know via a comment.

The finished project was much tidier than the first build but still hardly a professional finish! It does however work perfectly and the GPS requires no user intervention!

Power Supply built into small project box




DC/DC 5V Power Supply for in car PPC/GPS

Click here if your looking for the updated version of the DC/DC 5 volt power supply

I had a serial GPS mouse lying around (Thanks Alex) and my boss was kind enough to give me a retired HP Ipaq 2210 pocket PC from work. The 2 combined and I had a pretty reasonable touch screen car navigation system. Only problem was a power supply.

I didn’t want to use a cigarette lighter adaptor because I would have wires going everywhere; I wanted it hard-wired so the the GPS mouse sits on the dash with the cable disappearing down behind and a single thin cable coming out from the centre console for the Ipaq. I also wanted the GPS mouse running full time so there was no delay when it was searching for the satellites but I only wanted the IPAQ to be powered when the ignition was on.

I made 3 attempts before I was successful. First was 2 LM7805 5volt regulators. These got way too hot even with a heatsink; I would have needed a huge heatsink. Second attempt was the contents of 2 cigarette lighter to USB adaptors supposedly able to deliver 1AMP; yeah right! These things just about burst in to flames when I turned on the IPAQ! The third and successful attempt uses a LT1074 switching regulator and is detailed below.

The LT1074 was provided as a sample from Linear Technology, which is great since they cost about $NZ40 to order from RS!

The schematic is just the reference one from the LT1074 datasheet. schematic

I couldn’t find exact matches for all the components in the reference schematic.

Here’s a list of parts I used
Electrolytic 470uF (25v)
C2: Green Cap 0.01uF (This was a guess! All I really new is that it wasn’t an electrolytic because the schematic shows no polarity symbols!)
C3: Low ESR electrolytic 220uF (25v) (The application noste AN35 said to use low ESR and place it very close to the the LT1074).
MBR6745: This a SCHOTTKY-BARRIER RECTIFIER DIODE the recommended MBR745 is rated at 7.5Amps I used an ERC81-004 rated at 3Amps. Robbed from an old dot matrix printer PSU.
R1:I couldn’t find 2.8K @1% so I used 2x 5.6K @1% in parallel; both 1/2watt.
R2:2.2K @1%; 1/2 watt
R3:2.7k @5%; 1/2 watt
L1: This is of unknown value; robbed from an old dot matrix printer PSU. The application notes AN35 describe a rather humerus “alternate” method of selecting and inductor: (Click to read)


I haven’t done any PCB etching since high school so I thought I’d give it a go. I used Eagle CAD PCB design software which allows boards 100mmx80mm to be designed using their freeware version. Eagle is a bit clunky and counter-intuitive but once you get the hang of it, it’s really very good.


I followed the laser printer method for my etching as described in this instructables article.

1.Print the design to some shiny paper. (Thanks to ASB Bank!) Clean up the copper board with some 1200 sand paper
Iron On Design

2. Iron on the design
Iron On

3.Soak the board for 10Mins in cold water

4.Clean the paper off the board
Clean Up

5 Make up some etchant with Hydrochloric Acid and Hydrogen peroxide (Be careful!)
Etch Solution

6.Etch the board

7.Etching Complete

8.Drill, holes, add components and solder

9.Test. Wow! It works! It has two +5v outputs, one is always on for the GPS the other is switched on via the relay at ignition.

That’s it! A bit of shame I don’t really understand how it works! It does the job though and with very little heat.