Sure, no problem, let me clarify: the $119 version is the assembled board + software (including the Arduino clone) with no sensors. The $219 version is the assembled board in a case with a mounted alcohol sensor for the Breathalyzer feature + software. The $219 is the turn key version meant for non-technical users to get up and running quickly. Hope that helps, thanks.
Actually I'm a bit confused by this, because the DIY Magic Mirror site provides two links. The one I was talking about for $219 was the Sensor Hub available from MagicMirror.com. The one you are talking about for $119 says Magic Mirror Kit Version (Arduino Equivalent) available from SeeedStudio.com ... I'm not too sure what the difference is.
Hey Duane, thanks for the comments. The reason for the component selection was twofold. Firstly, Max tends to come up with these crazy ideas when the shops are closed so I often have to make do with what I’ve got in stock, and second and probably more relevant to a project like this, is component availability around the world and never knowing exactly what constructors will have to hand. For example, those 78 regulators are as common as chips in most places and have the advantage that besides being almost bomb proof and you can bolt them to a heat sink. This is a useful feature if you’re going to be running the unit from a PSU that puts out a highish voltage; perhaps an old Laptop PSU for example; these often put out in excess of 18v. The 12v regulator feeds the 5v one to help keep its operating temperature down but there’s a jumper that can be changed to bypass the need for this regulator if it’s not required. For my own use, a nice switching regulator IC would have been ideal, but they can be difficult for some people to get hold off. The MAX232 chips are also an interesting conundrum. For readers that don’t know, the actual MAX232 is available in several flavours. All need 5 external capacitors to work, but some require 100nf and others 1uf. You can replace the 1uf capacitors with 100nf capacitors if you have a version of the MAX232 that allows it; there’s room on the board, or just leave the 1uf’s installed and they will work with any MAX232 you use.
Hi Duane -- that's a great suggestion -- I'll order one of those PIR motion detectors from Adafruit. The reason Joe put both 12V and 5V regulators on the board was to make my life easier -- but he told me that he's also made the board with a jumper so I can omit the 12V regulator. I'm really looking forward to getting this up and running -- watch this space for Part 2...
You could make the 12V definitely not required and simplify the circuit a bit by using one of the common 5 volt PIR motion detectors. Adafruit and a number of other hobby electronics suppliers sell 5 volt detectors for around $10.00. You could probably also change the regulator to a TO-92 form factor to drop the cost a bit and reduce the space requirements. I've used a couple of inexpensive MAX232 type chips with ceramic caps, so that could drop the size and cost a bit more too.
It sounds like a very fun project. I could envision having one of these in the kids' bathroom that shows my face saying "don't forget to brush your teeth."