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AN #130 - Using the AD7895-10 Bipolar AD converter Print
Using the AD7895-10 Bipolar AD converter

This application note is written by Madhav Tenneti, Managing Director of Spectrochem Instruments Pvt. Ltd.

I have just finished interfacing an Analog Devices AD7895-10 Bipolar AD converter using BASCOM. The results were extremely good. I have calibrated the system using a YOKOGAWA CA11 (Handy Cal) Calibrator. The AD7895 offers 192KHz conversion speed. I thought this might interest people working on Data acquisition. I am providing the Source code, Circuit in PDF, & hex file.

Download the  Circuit AN7895.PDF (this is not the pdf of the chip)

Download the source code and hex file

'%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Ad7895 -10 Bipolar Adc %%%%%%%%%%%%%%%%%%%%%%%
'Written by... Madhav Tenneti
'Spectrochem Instruments Pvt. Ltd.
'B-23 Huda Complex, Saroornagar
'Hyderabad, Andhra Pradesh
'500 035 INDIA, Ph 91-40-24053341, 24053342 or 24146308
'URL: www.spectrochemindia.com
'Email: madhav@spectrochemindia.com
'IIC ADC using AD7895-10
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Hardware setup %%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Waitms 100
$crystal = 8000000
Baud = 9600 ' Powerup delay for lcd Initilization
Config Lcd = 16 * 2 'A 16 column by 2 row LCD display
Config Lcdbus = 4  'Configured in 4 bit mode
Config Lcdpin = Pin , Db4 = Portb.4 , Db5 = Portb.5 , Db6 = Portb.6 , Db7 = Portb.7 , E = Portb.1 , Rs = Portb.0
Config Pind.3 = Output 'Connected to convert pin of AD7895
Config Pind.4 = Input ' Connected to data pin of AD7895
Config Pind.5 = Output 'Connected to Clk pin of AD7895

Convrt
Alias Portd.3
Busy
Alias Portd.2 ' The busy pin of AD7895 is connected to Int0(PortD.2)
Enable Interrupts 'Enabling Global interrupt
Enable Int0 'Enabling INT0
On Int0 Cnvrt 'On interrupt branch to isr
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%% Variable Declarations %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Dim Port_data As Integer , Volt As Single , Ready As Byte , Msb_chk As Byte
Dim Tmp As Byte , I As Integer , Finl_volt As String * 8
Dim Avg1000 As Single , Temp As Single
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%% Sub routine declarations %%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Declare Sub Splash()
Declare Sub Ad7895()

'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%% Main Program %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Waitms 100 'Delay after lcd initilization
Call Splash
Do
 
Call Ad7895
 Temp
= Avg1000 * 100
 
Cls
 
Lcd "Temp: " ; Temp
 
Lowerline
 
Lcd "Avg1000: " ; Finl_volt
 
Waitms 200
 
Print Finl_volt
Loop
End
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%% Sub routines %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
'**********************
'*** Welcome Screen ***
'**********************
Sub Splash()
 
Cls
 
Lcd "Spectrochem"
 
Lowerline
 
Lcd " Instruments"
 
Wait 2
End Sub
'*************************
'*** AD7895-10 Convert ***
'*************************
Sub Ad7895()
 
Set Convrt
 
Waitms 10
 
Reset Convrt 'initiate Conversion
 
Waitus 1
 
Set Convrt
 Avg1000
= 1 ' 1000 reading average
 
For I = 1 To 1000
 
If Ready = 1 Then
 
Shiftin Pind.4 , Portd.5 , Port_data , 1 , 16 'Capture 16 bit data
 Msb_chk
= High(port_data)
 Tmp
= Msb_chk And &H08 ' Check for 2's compliment
 
If Tmp = 8 Then
 Port_data
= Port_data - 4096 ' Conversion to signed data
 
End If
 Volt
= Port_data * 0.0048828 ' Applying transfer function for voltage
 Avg1000
= Avg1000 + Volt
 Ready
= 0
 
Enable Int0
 
Set Convrt
 
End If
 
Reset Convrt
 
Waitus 1
 
Set Convrt
 
Next
 Avg1000
= Avg1000 / 1000
 Finl_volt
= Fusing(avg1000 , "#.####") 'Formatting data for appropriate display
End Sub

Cnvrt
:  ' Interrupt service routine
 
Disable Int0
 Ready
= 1
Return