Contents:

• Simple A to D:

• Intro
• Test Circuit diagram
• Code
  • Test Code
  • Modification to test code
  • Data Logging
    • - How to capture the data
    • - How to display it in Excel

• A Slightly more complex Datalogger
• Datalogger with Graphics

I have a number of ideas involving the use of A to D converters, including a simple thermometer, and a Data Logger.

Below is a sample circuit to show how easy it is to use a Serial AD chip.

The circuit simply reads the voltage at the chip's input (Provided by the 47k variable resistor), and displays the digital value (in Decimal and Hexadecimal) on my 5 digit LED display. A little bit of maths and you could easily display the actual voltage (eg: 255 = 5V, 127 = 2.5V, 000 = 0V), but this gives you the idea.

The code is a simple modification of one of the sample codes in the data sheet for my 5 digit LED display. The actual ADC part of the code is very simple. The pdf for the AD chip is available from Texas Instrument's web site. Folks in NZ or Australia, Dick Smith has this chip in stock.

Circuit Diagram:

Code: 

Step 1: Test program - simply displays the actual byte sent from the ADC

Step 2: Modify code to display the actual voltage.

Step 3: Let's log some data!

'{$STAMP BS2}   '*****DECLARE VARIABLES***** 'DATA for the Display's Character Lookup Table data 63,6,91,79,102,109,125,7,127,111 '0-9 data %01110111,%01111100,%00111001,%01011110,%01111001,%01110001 'A-F (EEPROM address 10 to 15) 'CONSTANTS dispclock CON 6 'P6 = clock to 4094's pin 3 dispdata CON 5 'P5 = Data to 4094's pin 2 ADclock CON 13 'P13 = Clock to TLC548 ADdata CON 14 'P14 = Data from TLC548 ADenable CON 15 'P15 = CS on TLC548 Low = enabled 'VARIABLES strobedigit var nib 'a four bit variable used to determine which digit to update character var byte 'the data to send to the display datafromAD var byte 'the data from the PC a var byte 'just a FOR loop variable nibble var nib 'used to store the lower or upper 4 bits of "datafromAD" divider var byte '*****MAIN PROGRAM***** HIGH ADenable 'Set up the display Gosub blankdisplay ReadAD: LOW ADenable SHIFTIN ADdata, ADclock, MSBPRE, [datafromAD] HIGH ADenable GOSUB DisplayASCIIHEXcode goto ReadAD DisplayASCIIHEXcode: nibble = datafromAD 'transfer lower 4 bits of byte to nibble read nibble, character 'lookup data in table to send to the display strobedigit=0 gosub loadregisters nibble = datafromAD >> 4 'transfer upper 4 bits of byte to nibble read nibble, character 'lookup data in table to send to the display strobedigit = 1 gosub loadregisters DisplayASCIIDECIMALcode: 'Figure out hundreds unit nibble = datafromAD/100 strobedigit = 4 read nibble, character gosub loadregisters 'Figure out tens unit divider = nibble*100 divider = datafromAD-divider nibble = divider/10 strobedigit = 3 read nibble, character gosub loadregisters 'Figure out ones unit divider = datafromAD/10 divider = divider*10 nibble = datafromAD - divider strobedigit = 2 read nibble, character '(turn on decimal point to seperate Dec from Hex on the display) character = character+%10000000 gosub loadregisters return blankdisplay: SHIFTOUT Dispdata, Dispclock, msbfirst, [0] 'blank display for a = 0 to 4 pulsout a,1 'Strobe each digit next return loadregisters: SHIFTOUT Dispdata, Dispclock, msbfirst, [character] 'Send data to the display PULSOUT strobedigit,1 'Strobe required digit to display the data return

Simple Volt Meter...

'{$STAMP BS2} 'This version displays the actual voltage, rather than the digital value from the ADC '*****DECLARE VARIABLES***** 'DATA for the Display's Character Lookup Table data 63,6,91,79,102,109,125,7,127,111 '0-9 'CONSTANTS dispclock CON 6 'P6 = clock to 4094's pin 3 dispdata CON 5 'P5 = Data to 4094's pin 2 ADclock CON 13 'P13 = Clock to TLC548 ADdata CON 14 'P14 = Data from TLC548 ADenable CON 15'P15 = CS on TLC548 Low = enabled 'VARIABLES strobedigit var nib 'a four bit variable used to determine which digit to update character var byte 'the data to send to the display datafromAD var byte 'the data from the AD Voltage var byte a var byte 'just a FOR loop variable nibble var nib 'used to store the lower or upper 4 bits of "datafromAD" divider var byte '*****MAIN PROGRAM***** HIGH ADenable 'Set up the display Gosub blankdisplay ReadAD: LOW ADenable SHIFTIN ADdata, ADclock, MSBPRE, [datafromAD] HIGH ADenable ConverttoVolts: Voltage = (datafromAD * 100)/510 'debug dec Voltage GOSUB DisplayVoltage goto ReadAD DisplayVoltage: 'Figure out hundreds unit nibble = Voltage/100 strobedigit = 2 read nibble, character gosub loadregisters 'Figure out tens unit divider = nibble*100 divider = Voltage-divider nibble = divider/10 strobedigit = 1 read nibble, character '(turn on decimal point) character = character+%10000000 gosub loadregisters 'Figure out ones unit divider = Voltage/10 divider = divider*10 nibble = Voltage - divider strobedigit = 0 read nibble, character gosub loadregisters return blankdisplay: SHIFTOUT Dispdata, Dispclock, msbfirst, [0] 'blank display for a = 0 to 4 pulsout a,1 'Strobe each digit next return loadregisters: SHIFTOUT Dispdata, Dispclock, msbfirst, [character] 'Send data to the display PULSOUT strobedigit,1 'Strobe required digit to display the data return

Data Logging:

In order to log data, you can do it two ways.

1. Store data in memory on your microcontroller board and download later, or

2. Send data, as it is collected, to a PC.

Then - display the results.

Here is how I set up my test circuit, for option 2, to log the voltage every second as I adjusted the Variable resistor, and display the data in Excel on my Mac and Windows PC.

a). Firstly, in order to present the data in a format that Excel can understand, you need to create a "Comma separated values" file. This is a text file where commas separate the field values.

b). Use Hyperterminal to receive data from the Stamp, and turn on Text Capture.

So, to display something like the following table in Excel:

Time	Voltage
1	0.02
2	0.50
3	3.70
4	4.70

Your text file will need to look like this:

Time,Voltage

1,0.02

2,0.50

3,3.70

4,4.70

 

The code below will do this. This version displays the voltage on my 5 digit LED module, and the data is sent out the serial port, formatted as per the requirements above.

'{$STAMP BS2} 'This version displays the actual voltage, rather than the digital value from the ADC, and sends the data to a PC for logging. '*****DECLARE VARIABLES***** 'DATA for the Display's Character Lookup Table data 63,6,91,79,102,109,125,7,127,111 '0-9 'CONSTANTS dispclock CON 6 'P6 = clock to 4094's pin 3 dispdata CON 5 'P5 = Data to 4094's pin 2 ADclock CON 13 'P13 = Clock to TLC548 ADdata CON 14 'P14 = Data from TLC548 ADenable CON 15'P15 = CS on TLC548 Low = enabled 'VARIABLES strobedigit var nib 'a four bit variable used to determine which digit to update character var byte 'the data to send to the display datafromAD var word 'the data from the AD Voltage var word time var byte a var byte 'just a FOR loop variable nibble var nib 'used to store the lower or upper 4 bits of "datafromAD" divider var byte '*****MAIN PROGRAM***** HIGH ADenable 'Set up the display Gosub blankdisplay time=0 pause 2000 serout 16,396, ["Time,Voltage",13] ReadAD: LOW ADenable SHIFTIN ADdata, ADclock, MSBPRE, [datafromAD] HIGH ADenable PAUSE 1000 ConverttoVolts: Voltage = (ABS(datafromAD) * 100)/51 GOSUB DisplayVoltage time= time +1 goto ReadAD DisplayVoltage: 'Figure out ones unit nibble = Voltage/100 strobedigit = 2 read nibble, character '(turn on decimal point) character = character+%10000000 gosub loadDisplay serout 16,396, [dec time,",",dec nibble,"."] 'Figure out first decimal place divider = nibble*100 divider = Voltage-divider nibble = divider/10 strobedigit = 1 read nibble, character serout 16,396, [dec nibble] gosub loadDisplay 'Figure out second decimal place divider = Voltage/10 divider = divider*10 nibble = Voltage - divider strobedigit = 0 read nibble, character serout 16,396, [dec nibble,13] gosub loadDisplay return blankdisplay: SHIFTOUT Dispdata, Dispclock, msbfirst, [0] 'blank display for a = 0 to 4 pulsout a,1 'Strobe each digit next return loadDisplay: SHIFTOUT Dispdata, Dispclock, msbfirst, [character] 'Send data to the display PULSOUT strobedigit,1 'Strobe required digit to display the data return

 

Here is an example of the captured data.

How to display in Excel:

 

Within Excel, start recording a Macro. Open your text file, and follow the wizard to get your data displayed correctly.

You can create graphs of your data as in the screenshot below.

 

Now, everytime you run the Macro, you can easily collect data from your A to D circuit.

 

 

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A complete working datalogger.

• The circuit on this page is made up from circuit examples on other pages on this site.
• The circuit diagram is below, and I've included some sample screen shots of collected data.
• The circuit shows a Temperature sensor wired up. You can easily connect whatever you want as a transducer...
• For full details on each device, have a look at the datasheets for them, which are easy to find on the Internet.

The code to make this all work is below.

Notes:

• The code does not include code to read or write from the RTC, as I started to run out of space on the BS2 to include that code. A BS2e will have enough EEPROM space to store the datalogger code and RTC code.
• Code to read and write to the RTC is on my I2C page.
• This code is specifically for the circuit above, using the temperature sensor. To just measure voltage, you'd need to change the code slightly. I'm sure you can figure it out, if not, . I will, once I get my hands on a BS2e, change this page to show the code for the RTC, and other improvements (like autosensing what type of probe is plugged in).
• You will need to burn an EEPROM for EEPROM_1, that contains all the messages, etc. used for the LCD. You can either figure out how to do this yourself, using the map below, or for details.

 

TABLE 1 - Memory Map of the 24C02 at Device address 002 on the I2C BUS

00

01

02

03

04

05

06

07

08

09

0A

0B

0C

0D

0E

0F

00

L

e

n

n

a

r

d

E

l

e

c

t

r

o

n

10

i

c

s

w

w

w

.

l

e

n

n

a

r

d

.

n

20

e

t

.

n

z

F

i

r

m

w

a

r

e

v

1

30

.

0

0

0

9

/

0

2

S

a

m

p

l

e

40

M

e

m

o

r

y

A

b

o

u

t

S

a

m

50

p

l

e

R

a

t

e

i

s

A

d

j

u

s

60

t

O

K

O

n

B

70

o

a

r

d

M

e

m

o

r

y

S

t

o

r

e

80

D

o

w

n

l

o

a

d

P

90

r

e

s

s

G

o

w

h

e

n

r

e

a

A0

d

y

D

o

w

n

l

o

a

d

i

n

g

.

.

.

B0

o

f

s

e

c

m

i

n

h

o

u

r

0E

11

C0

15

15

15

11

15

1F

0E

11

11

11

11

11

1F

1F

0E

1F

D0

1F

1F

1F

1F

1F

1F

0E

11

1F

1F

1F

1F

1F

1F

0E

11

E0

11

1F

1F

1F

1F

1F

0E

11

11

11

1F

1F

1F

1F

0E

11

F0

11

11

11

1F

1F

1F

18

14

14

14

1C

01

0A

04

00

00

	Display messages
	Custom LCD characters
	User settings

The code is here.

---

 

<TO ADD LATER>

There are two ways to collect data from the Datalogger.

• As the data is sent in a .csv file format, you can use Hyperterminal and capture the text, then use Excel to manipulate the data.
• Use my Datalogger Application for Windows or Macintosh
  • Windows version - Serial Port support only
  • Mac versions - USB Support, Serial Support (if using the USB version for Mac, download the USB extension here).

</TO ADD LATER>

 

---

 

Improvements:

• Auto sense the type of sensor so that there is no manual setting or scaling required.
• Add multiple ADC's, so we can measure may things at once (eg: Temperature, Light, Humidity, etc.)
• I also have a graphics capable datalogger here.

 

---

 

Screen shots:

All the data for these examples was collected by downloading the data from my datalogger's memory to Hyperterminal (or a similar Mac terminal emulator) using text capture mode, then the captured text file was loaded in to Excel and the chart wizard used to create the graphs.

---

• Temperature in the lounge at home over a 21 hour period...
  • Conditions: A nice warm, sunny day in Wellington, with a mild breeze.
  • Start time 2pm Saturday
  • Samples every 5 minutes (256 samples x 5 minutes = 21.3 hours)
  • Finish time, approx 11:20am Sunday (This is where the RTC code would come in handy - getting exact times).

You can see that the temperature went up and down a bit during the day. It can get hot in the lounge, and opening a window, and the door to the balcony helped cool the room down (until the wind stopped...). The Time along the X axis was a simple calculation in Excel.

---

The next two examples use the modified code (just displaying the actual voltage).

 

• light level during the day from 4.30pm until 8.46pm...
  • Trasducer: A Solar panel.
  • Conditions: Very cloudy and windy
  • Start time: 4.30pm
  • Samples: 1 minute samples (256 x 1 min samples = 4 hours and 16 minutes
  • Finish time: 8.46pm

You can see the light level going up and down as clouds passed by overhead. Around about 6.30pm, is when the sun started to disappear behind the hills of Crofton Downs, and from 7pm to 7.40pm more peaks and throughs as clouds cleared then gathered again, then from around 7.50pm, the sun started to set altogether.

---

• Discharge of a capacitor over 4 minutes and 16 seconds (256 1 second samples)...

This is a chart created in Excel. A .csv file is imported to Excel with the data as read from the Datalogger's memory, then in Excel, a simple calculation is performed to get the actual voltage that the data represents.