As mentioned in Part1 of my review of expEYES Jr. we are looking at a very capable ‘science experimental kit’ both in terms of physical experiments and programming. The range of experiments makes the device worth £50 in my opinion, there are however room for development and improvement – particularly in the documentation / user manual. It would for time constraints be impossible to cover every possible experiment in this review – but lets go through a few different exercises to give you a flavor. As a start once software is installed i would recommend doing the first basic exercise just to verify the device. And for it’s flaws I would highly recommend that you DO follow the manual – against geek nature , I know. For the record I am running this review on Linux Mint installed on a MacBook Pro.
So let us go through a very basic measuring a voltage output from PVS on IN1, wire up the unit as shown in picture. The Terminal screws are a bit stiff at times – this no doubt will be rectified in the next edition. Find the ExpEyes application and open up.
Lets do something a little bit more advance – we’ll move on to Sinewave and Squarewave, hook up unit as shown in picture below:
‘Drag’ A1 to channel 1 – set PVS to 1 Volt and you should see this Sinewave across your screen.
OK let’s combine this with a square wave , assign SQ1 to CH2 by dragging the SQR1 tag to channel 2 , you should now have 2 traces running a cross your screen like this :
We we have also added a Fourier Trace in right hand corner, yes I told you this kit is impressive.
Right a fun thing for kids to do is to measure ‘Body Resistance’ – hold a probe in each hand , hooked up to an oscilloscope – science has gotta be fun ! We’re running a low voltage of 4V across 2 probes from PVS and A2, hook up your unit as shown below with a 200K Ω resistor:
So my young assistant is holding the 2 open ended wires / probes from A2 and PVS (4V) , essentially measuring his body resistance between his arms /chest. I must stress we are using a LOW voltage of 4 Volts here :p The resulting trace can be seen below:
Last but not least we need to explore the programming capability in this kit , specifically Python. In order to use this we need to install the NumPy modules – follow all software installation steps here. As usual we’ll start of with a set of easy commands to verify the expEYES module: Start Terminal and initiate python; type python and hit return. To initiate the expEYES module and measure capacitance type the following commands , hit return between each (do not add spaces or >>>, these will appear automatically in python) :
>>> import expeyes.eyesj
You will now have a readout of stray capacitance on port IN1, you should see this in terminal :
Let’s try some plotting / tracing in Python – and I’m not talking conspiracy theories here , code is already KING !! First hook your module up as seen on pic below , SINE must be connected to A1. Let’s plot a SINEwave in Python using the expEYES module as wave generator and input: type the following code in terminal, hit return between each line:
>>> p.set_state(10.1) #set OD1 to 'high'
>>> print p.set_voltage(2.5)
>>> print p.get_voltage(1)
>>> from pylab import *
>>> t,v = p.capture (1,300,100)
>>> (plot t,v)
You should see this trace across your screen :
OK so what has all this got to do with Raspberry Pi ?? Well the expYES software will actually run on a Raspberry Pi – however buggy and processor hungry at the moment. I am in dialog with PiSupply to iron out the gremlins & I will soon be passing this kit on to someone with expert programming skills for further evaluation. As said there is clearly room for improvement with the expEYES Jr kit – the only reason I’m being ‘nice’ about it because of the incredible potential for a great learning resource. There has already been a lot of careful thought and clever engineering poured into the development of this kit – it is not just a ‘mayfly’.
Watch this space for further developments !