Help reading serial data into chart

Hi, Ive got a windows form made in vb2010 and i want to use the chart feature.
at the minute Ive got a string coming in from the serial port that is a temperature in this format "20.0" etc where it is a floating point to one place of decimal.
I am not sure how to get it to display properly, im using this code which Ive tried to adapt, with no success.
The graph moves along but wont show the correct temperature values probably because it is a string im converting to. I have tried converting to intger and actually changing the temperature format to an integer value but i get an error about being unable to cast when the value is greater than infinity.
Any help would be greatly appreciated. Thanks

Dim temperature As String = SerialPort1.ReadExisting
Chart1.Series("Series1").Points.AddY(temperature)

Firstly, have you confirmed you are reading accurate data from the port even though it is a string? If not, start there. make sure that if you should read 20.0 degrees you serial port is returning "20.0"
<edit>
After rereading your post, it sounds like you are.
</edit>

Normally when you are charting real world data you do so with the x-axis having time unit of some sort; either an absolute time being when the point was taken, or a relative time like "how long has it been since the first point was taken". Either way, you should be adding an x and y value rather than just a y value.

The AddY method adds a new Y value to the end of the points collection and in some cases is meaningless to the chart. You should probably be using the AddXY method instead.

Try this...

Code:

---

dim temperatureString as string = SerialPort1.ReadExisting
dim temperature as double
if double.tryparse(temperatureString,temperature) then
    Chart1.Series("Series1").Points.AddXY(Now,temperature)
endif

---

Even with a chart series configured to default settings, that code should display your data provided you have good data.
kevin

Quote:

---

Originally Posted by kebo

Firstly, have you confirmed you are reading accurate data from the port even though it is a string? If not, start there. make sure that if you should read 20.0 degrees you serial port is returning "20.0"
<edit>
After rereading your post, it sounds like you are.
</edit>

Normally when you are charting real world data you do so with the x-axis having time unit of some sort; either an absolute time being when the point was taken, or a relative time like "how long has it been since the first point was taken". Either way, you should be adding an x and y value rather than just a y value.

The AddY method adds a new Y value to the end of the points collection and in some cases is meaningless to the chart. You should probably be using the AddXY method instead.

Try this...

Code:

---

dim temperatureString as string = SerialPort1.ReadExisting
dim temperature as double
if double.tryparse(temperatureString,temperature) then
    Chart1.Series("Series1").Points.AddXY(Now,temperature)
endif

---

Even with a chart series configured to default settings, that code should display your data provided you have good data.
kevin

---

Hi Kvin,
Thank you for your reply and help.
The values are correctly read in by the serial port as they are displayed in a text box. The code you posted seems to work, it seems as though the update interval for the chart is really slow. it takes forever to plot a change.
i have this code so far.
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
' Dim temperature As Int16 = SerialPort1.ReadExisting()

'Dim temp_out As Integer
'temp_out = CInt(temperature)

' Dim temperature As String = SerialPort1.ReadExisting
Dim temperatureString As String = SerialPort1.ReadExisting
Dim temperature As Double
If Double.TryParse(temperatureString, temperature) Then
Chart1.Series("Series1").Points.AddXY(Now, temperature)
End If
rtbReceived.Text = temperatureString

Once again, thank you for your help with this issue. I appreciate it

what is the timer interval?

at what rate is your hardware sending temperature updates?