Cables for Resmed Astral 150 and Resmed Connectivity Module (RCM)

Introduction

In this article we'll go over how to get the cables and power supply you need to hook up the RCM to your Astral from Amazon for about $30 and probably overnight.  Some readers may be trying to hook up their modem but it's still not working, and we have a troubleshooting guide just for you.

Let's be brief:  The Astral 150 is a flexible ventilator and the RCM is a cell based modem that let's your respiratory therapists and doctors see how the device is performing remotely. The problem is that the USB cable and power supply are a little non-standard and could take weeks to get if ordered from ResMed or your local CPAP supplier. 

I'm afraid I don't have advice for you if you have another type of ventilator, but maybe once you see how we build the two cables for these it will be easy for you as well.

 

Connecting

Once you have the right parts installation is easy.

1. Connect power to the modem.  
2. Wait for the power light and signal strength to light up. 
3. Make sure the ventilator is already on. 
4. Plug in the USB cable. 

Take a look at the picture, below, which is what the RCM looks like when everything is working.  There's a little blue LED above "Vent. Input." You may not see it well with bright lighting. That should start to light up immediately after step 4, if not you are using the wrong cable and probably plugging it into the wrong port.  If this isn't working immediately keep reading the next section which probably has a solution for you. 

 

USB Troubleshooting

Let's go over the connections on the back of the Astral 150, below. The Astral actually has two USB connectors (#5 and #6, below) but only one of them works for the RCM.  Much as you probably want to, you can't use #5 for the RCM, I'm sorry.  Number 5 is just for USB memory sticks.  The connection you want to the modem is #6, and it's a different USB connector type than the modem has.   Frustrating as hell, right? 

Again, the big, square USB connector is not usable for the RCM. 

 

With the right cable (see below) plugged into the right port you'll get a flashing light for a few seconds and then solid blue when the handshaking is finished and you are good to go.

Just tell me what to buy!! 

 OK, OK!  Here they are:

• USB data cable
• 24V power adapter with polarity inverter
  

Check the length on the data cable before ordering, make sure it's long enough so you can put the modem in a convenient location. Read below for more details on using alternatives.  

RCM Power Adaptor

The next frustrating part is the power adapter the modem needs.  This modem uses a 24V / 200 mA ( about 5 Watt ) adapter, which is a little unusual for most home devices, but incredibly it has the polarity reversed from the common convention.  Instead of (-) being on the outside it is on the inside for the RCM and we have to solve that problem one way or another.  I'm going to give you two options.  One for people with no tools or skills and one for people with a multi-meter and wire stripper already in their bag. In a post-covid19 world with unreliable supply chains this may be helpful.  Done correctly the two are equivalent.  Go with the first option unless you can't find them in stock.

Easy Power

It is super frustrating Resmed chose to use a non-standard polarity for what would otherwise be a very simple part to find, but whatever.  Here is the part you need from Amazon: 

 

 

This checks off all the boxes you need:

• 24 V
• Polarity inverter (see the little cable at the top, with both a male and female plug?)
• More than 5 Watts 

When you get it, set the V to maximum, attach the polarity inverter and you are done.  

Power for the DIY kind of person

Not really a cost saver, but it may be easier for you to find a standard 24V supply like this one, and then  hack it to the right configuration.  Also be sure to check the length of the cables on any adapters you buy to make sure it works for you.

 

 

The plug is exactly the right size, 5.5 x 2.5 mm, but the (+) and (-) are reversed.  It comes with an adapter for bare wires, which we can hook up with pig tails like these:

 

 

You need to reverse the polarity, which should be red (above) to minus, but if you lack a way to check DC voltages, you can just try it.  You won't hurt the modem.  Plug it in and the power light should be on in 2 seconds.  If not, reverse and try again.  You are half way there.  Assuming you have a 24V, 200 mA adaptor already then maybe you just need a plug. 

 

USB Cables

One Cable to Rule them All

There are in fact USB mini B to micro B cables available, like this one: 

 

This is by far the simplest solution.  Make sure you get the right length, one is shorter than a foot, and the other is 1m. The main reason not to go with this option is if you want to run a longer USB cable, in which case read below for more options.

 

If you have a digital camera somewhere gathering dust you might want to scavenge the box it is in to see if you have one already. 

Gender Bender

Fortunately, chances are really good, if you've not thrown away your cell phone charger cables in the last couple of years, you have a cable that fits the modem, and one that fits the ventilator.  If this is the case you just need a gender changer like this one:

 

 

Plug one cable into each device, and use this in the middle.  Voila! In case you kept everything labelled in your box you will need a mini B cable and a micro B cable.  I don't ever remember which is which, but that's what you need, unless you want to go with a pig tail and gender changer combo, below. 

Lastly

Just in case you really are frugal, and already have the mini B cable that plugs into the modem you can use a mini B to female adapter like this one. 

Conclusion

I hope that if you are in the situation I was in you'll find this useful, and if you have other types of power and cabling issues this post has given you some ideas on how to solve them cheaply.