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.
The screen here shows a 1V output from PVS with IN1 used as input – we have used CH2 to show trace.
Use jumper cables / clips provided to connect PVS to IN1.
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.
Sinewave output from A1 (analogue port).
Hook up SINE port to A1 (analogue) as shown – yes you can ‘HotPlug’ 😛
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 :
SINE wave and Square wave running parallel on Cannel 1& 2. Fourier Trace Spectrum analysis window in right hand corner.
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:
Connect a 200K Ω resistor between A2 and GND , loop A1 and PVS with a wire – then add 2 open ended wires from A2 and PVS.
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:
Constantly variable trace showing resistance from input A2 (analogue).
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 :
Measuring stray capacitance on port IN1, 3 repeats to show variation over time.
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 :
Python is here used to code the entire experiment; not just generating the SINEwave but also to plot the output from A1.
Hook SINE up to A1 (analogue) & OD1 to IN1 , we will set PVS to 2.5V and do SINE trace from A1.
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 !