Blog Posts tagged ‘wireless’

If you have been following this blog for a while you might have seen my previous article on the portable, wireless IP kvm that we constructed a while back for datacentre use. This has proven to be an invaluable tool for remotely accessing machines instantly, in fact so invaluable that contention for its use frequently causes consternation. When I completed the last device, I made a list of how it could be improved in a future revision so when I decided we needed a new one, I thought I’d take care of some of the improvements I had planned.

To refresh your memory:

• remove covers of internal components to reduce space requirements and improve cooling
• align the wireless antennae in the middle of the case so cables from the wireless bridge are hidden
• reuse PCB mount points to screw the boards into the kit box, or use some sort of glue
• install a unified power supply for the wireless bridge and IPKVM

As you’ll see below, I have taken care of all of these concerns and more.

As soon as the wireless bridge and IPKVM hit my desk, the screwdrivers came out. I set about taking out the cases off the bridge and the IPKVM and seeing what the circuit boards were like.

As you can see, Linksys just use a miniPCI wireless card on the bridge and a couple of standard antenna cables. I wondered what might be under the copper shielding but I didn’t want to destroy anything too early on in the process so I had to suppress my curiosity.

The IPKVM circuit board is quite neat and tidy. A perfect candidate for removing the casing! At this point I inspected the boards to see what kind of power supply I’d need. The IPKVM takes 5v but the wireless bridge takes 12v. Jaycar had some nice small switched AC/DC power supplies which can output up to 25w at 12v. This is fine for the bridge but I’d need some sort of regulator for the IPKVM.

I started looking at voltage regulator components such as an LM7805, but most would only do up to 1A and the IPKVM is rated to 2A. It is of course possible to build a 2A regulator using two LM7805s and some supporting components but that would mean building a circuit board, finding a good circuit design and spending a reasonable amount on the components – LM7805s aren’t cheap! I decided to find an alternate solution.

Hobbyists frequently pack a lot of batteries in their remote control cars and planes and use tiny, lightweight voltage regulators to bring the voltage down from 14.4V to 5V which the motors require. These are easily found on Ebay for less than $10 and do the job perfectly, so I found one and pretty soon it was on my desk. Above you can see the size comparison with a standard coin.

After a trip to Jaycar, I had most of the remaining components, including an IEC power socket and 3-wire AC cable. With this connected to the power supply, we can easily connect the Wireless IPKVM straight to our APC power rails in the datacentre.

Here you can see the 12v 25W power supply. It is quite small due to it being a switch-mode design, and better yet has a cool little LED showing it is on. Sadly you can’t see this from outside the IPKVM.

It’s always good to cover all your bases when constructing like this, so I made sure to break out the old multimeter and check all the voltages. 12.2v unloaded voltage out of the PSU here is pretty good.

Note the awesome power LED on the PSU. The input/output terminals are the easy-to-use screw-down type. There also appears to be some sort of fine-tuning adjustable cap on the board which might change the output voltage but I wasn’t keen on making any changes.

Now it was time to test the output from the 5v regulator. Yes, right on 5.3v. I was pleasantly surprised by the glowing red LED supplied complimentary on the UBEC. The UBEC actually heats up a little bit despite being switch mode – supposedly it gets up to 92% efficiency which is great.

Voltage testing done, I prepared the 12v and 5v outputs with DC connectors suitable for the wireless bridge and IPKVM.

Here on my very neat testbench I have connected up the wireless bridge and IPKVM to the 12v and 5v outputs respectively. Lights are on! Everything seemed to be good at this point so I configured the bridge and IPKVM with final deployment settings, updated our documentation and started planning for building it all into a kit box.

Another trip to Jaycar later, I had my kit box. The form factor is a bit different to the mk I Wireless IPKVM – whereas the first incarnation was long, wide and flat, this one is a lot taller but narrower. Since we are stacking the boards and other components there will be less open space but hopefully the overall result will be neater and more compact. Above is the test placement of the PSU and IPKVM board. The IEC power connector nicely sits next to the PSU.

A bit of interest in the project generated around the office as it started to take shape. One coworker offered use of his dremel to cut the requisite holes in the box for connectors and another donated a couple of small 12v cooling fans to aid active cooling of the components rather than hoping passive cooling would do. This is probably a necessity, as the PSU and UBEC heat up a reasonable amount under load. I am assuming the IPKVM and Wireless bridge are no different.

I installed two fans both operating in the same direction so airflow would go through the box. It is completely sealed apart from these openings so having the fans both blowing or both sucking would be fairly disastrous. You can see that the IEC power socket sits nice and flush with the box wall. I’ve screwed it in, but also added copious amounts of hot glue

At this point I’ve got the power supply glued down, the fans in and the power connector secured. The IPKVM is glued down at the front and underneath, with a small section of cardboard to keep it leveled and some more at the back to brace it against the side of the box. This time around I crimped RJ45 connectors on a small length of Cat5 cut to measure so I didn’t have a huge amount of cable inside the box. Everything is ready for the wireless bridge!

As per my improvements list, I wanted to have the antennae concealed and this is just what I did. A bit of hot glue here and there and we have the antennae secured to the lid of the kit box, waiting for the mini-N connectors to be screwed in.

I was able to cut a few notches in the side posts of the kit box which allowed the wireless bridge to slot in nicely. I hadn’t even planned for this so it was a nice surprise. A bit more hot glue, and it is secure in place.

It would be a crime against humanity to not make use of blinkenlights wherever possible, so I drilled a few holes in the front of the box to allow the wireless bridge LEDs to poke through. Largely useless, since nobody will be watching it, but this is an important feature nonetheless.

Adorned with the official Blinkenlights warning, the Wireless IPKVM is now ready for use!

So there you have it. This project was definitely a success and there are already calls for me to rebuild the original Wireless IPKVM in a box like this one. I can’t think of any major improvements I’d like to make next time around, except perhaps for a transparent kit box with far more blinkenlights.