Schematic of hardware

This is a small visualization about how the klimabox probably goes look at.

Negative Supply voltage

Because we are going use the Adapters that are available in the laboratory we have only a positive voltage. For our project, the adapter needs to set to 12V.
But for the op-amps that we are using, we need a negatieve voltage of -12V.
We found a very simple circuit with a NE555. We builded it yesterday quickly and it works fine. We measured an output voltage of -11,62V. And the input voltage was 12,6V.
This is the circuit:

http://www.circuitsonline.net/schakelingen/139/voedingen/negatieve-spanning-met-ne555.html

PWM and Temperature sensor

Today was a productive day.
After a lot of testing of the PWM circuit, we had a good result.
The circuit is now working, but we only need to modify this.
We use now 4 single Op-amps (741) , in the future we go build this
with a quad op-amp IC.

This is a video of our signal:


And this evening, we are started with the LM35 Temperature sensor.
Here is also a first good result: we can read in the output of the sensor with the labjack.

This is the testcode where I send the measured signal on the input to the output but with a factor of 10 higher, so that it is easier to measure. Because the LM35 rise 10mV/°C.




---------------------------------------------



Public Class Form1
    Dim spanning As Double = 0
    Dim Checkken As Integer = 0

    Public Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

    End Sub


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Timer1.Start()
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        lj.LabJack.EAnalogIn(-1, 0, 0, 0, 2, spanning)
        lj.LabJack.EAnalogOut(-1, 0, (spanning * 10), 0)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Timer1.Stop()
    End Sub
End Class

---------------------------------------------
Video:

The circuit for making PWM

I told already that we are searching for a circuit to make a PWM signal with the analog output of the Labjack ( varies from 0 to 5 V ).

We found something that first makes a triangle waveform , and then makes with this triangle waveform makes a PWM signal.

Triangle waveform:

http://pcbheaven.com/circuitpages/Triangle_Wave_Generator/










PWM Generator:
http://pcbheaven.com/circuitpages/Voltage_Controlled_PWM_Generator/

But when we build it on a breadbord it seems that this is not quite stable.
So we ask our teacher of Electronics and he let us see a schematic in the handbook of Malvino. But we build it and tested it today while we have Electronics Lab. But this is only the part of making a triangle waveform.
But the circuit for making the PWM signal doesn't work yet. We need to do more tests.

The first tests

After talking with the teacher we knew that he is thinking about a temperature variation of about 2° in steps op 0,1°.

So this is normally possible with a small E10 light bulb of 3-5 Watt.

Yester we have done a first test with the Labjack. This was made a small program
in Visual Basic to turn on and off a LED on a digital output of the Labjack.
The reason of this test was that we want be sure that we can communicate from software to Labjack and turn on and off an output.
After installation of the driver and including the ".dll" we had the first test working.
This is our program code :
----------------------------------
Public Class Form1

    Private Sub Btn_aan_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btn_aan.Click
        lj.LabJack.EDigitalOut(-1, 0, 0, 0, 1)

    End Sub

    Private Sub Btn_uit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Btn_uit.Click
        lj.LabJack.EDigitalOut(-1, 0, 0, 0, 0)

    End Sub
End Class
----------------------------------

And this is how looks the frame with the buttons:

Also yesterday, we have removed 4 fans of old devices. So now we need only 1 more.
Today we have done the first tests with a fan and a small light bulb. We are now quite sure that it is possible to heat about 2° with a small light bulb. But the Labjack U12 doesn't support PWM, so we have to search for something else. We are now testing with a circuit that makes a PWM signal with a analog output of the Labjack.

Test of a small light bulb

A little test with a small light bulb told us that it is impossible to have enough heat.
We are now thinking of a light bulb of about 30 Watt in a E14 fitting.

Schematic of software

This is a small basic schematic of the software system.

The real object

Today, we have asked to the teacher what exactly the purpose is of the klimabox and with which materials we need to work.

The purpose is to design a nice control system. The perspex tube have a diameter of 50mm and have to be 10cm long.
The fan is a simple computerfan. (12V)
The heathingelement needs to be something like a small lamp. We are thinking about an old bicycle light. With a E10 fitting. And then 2 of these.
For the software we maybe go use a Labjack, this is easy for making an interface with usb.

Publication Project

We know now what our project is. We have to make our last choice: EA_Klimabox.
We have to make a cylinder of perspex(plexi) with a heating element and a fan.
The intention is making a circuit that holds the temperature in the cylinder constant.
And we need to design an application on the PC to show the working.