Interworld Electronics

Hardware

It states in the ADC-16 help file that the serial port requirements are:

The Palm Pilot has a 10-pin RS-232 serial connector, which can be used to communicate with a wide range of external devices.

Below is the pin-out description for the 10-pin serial edge connector:

From this it can be clearly seen that the ADC-16 can not be powered by a Palm Pilot alone.

To get round the power problems an adapter had to be built. This is quite small and can run of a 9 volt PP3 battery. The device fits in series with the serial cable.

Software

The ADC-16 has the following serial protocol:

• Switch RTS on and DTR off to provide power.
  
• Wait for more than 1 second for the ADC-16 to settle
  
• Send an single control byte to the ADC-16
  
• Wait for the 3 byte response from the ADC-16
  

The Palm Pilot operating system is unique and differs from Windows programming in many aspects.

There are a number of development tools available for writing Palm Pilot applications, for this particular example VFDIDE was used. It is a C++ compiler with a Visual form designer built in and can be downloaded free of charge from: www.vfdide.com

The structure of the program is as follows:

Start Application

Wait for start or exit signal

Open Serial port

Enter loop upon start signal

 

Send control byte to ADC16

 

Wait for response

 

Display result

 

Exit loop after 10 cycles

Close serial port

StopApplication upon exit signal

Once the program is broken down into blocks it is easier to code the individual parts

Start Application

static void StartApplication(void) {
Err Error;
FormPtr Frm;

Frm = FrmInitForm(frmadc16);
FrmSetActiveForm(Frm);
FrmDrawForm(Frm);

Open Serial port

The following code is used to open and setup the serial port:

error = SerOpen(SerIORef, 0, 9600);
if(error) {
FrmCustomAlert (AlertGenericAlert, strErrSerPortOpen, "can't open port","can't open port" );
SerClearErr(SerIORef);
return;}

SerIOConnected = true;
sstSetup.baudRate = 9600;
sstSetup.flags = serSettingsFlagBitsPerChar8|
serSettingsFlagParityOnM;

Send control byte to ADC16

The control bytes are defined in the help file, and are declaired at the start of the program.

For example 0X1F makes a request for a 16-bit single ended reading from channel1. These control bytes are used as so:

Wait for response

Once a request for data has been send it is neccessary to wait for a response. The duration of the delay between request and reply will depend on the resolution of the result:

SerReceiveWait(SerIORef, 3, 1000);
SerReceiveCheck(SerIORef, &nbytes);
anbytes = SerReceive(SerIORef, data, nbytes, 100, &err);
if (err != 0)
ret = false; else
ret = true;
SerReceiveFlush(SerIORef, 1);
return(ret);}

Display the result

The data is returned in three bytes, the first byte is the sign, the second is the most significant byte (MSB) and the third is the least significant bit (LSB). In this example the sign is ignored.

value = (data[1]<<8)+data[2];
volts = (2.5/65535)*value;

The problem now is that idealy the volts is floating point, however the Palm operating system does not have conventional ways of converting floating point values into strings.

FloatToString(volts, szvolts, 3);
StrCopy(szResult, "Voltage = ");
StrCat(szResult, szvolts);
WinDrawChars(szResult, StrLen(szResult),20,60);

The FloattoString function was taken from one of the many usergroups that offers assistance to palm programmers, it makes a rather neat solution to an otherwise tricky display problem.

Close serial port

It is essential that the port is closed after being used for a couple of important reasons:

• The serial port uses alot of power, keeping the time that it is open to minimum will keep battery usage down to a minimum
• Other applications that require the serial port will not function as access to the serial port will be denied

Results

Once the code has been compiled and downloaded to the Palm Pilot it is now possible to connect the ADC16 with aid from the power adapter.

Full code can be downloaded here: adc16.zip

References

ADC16 online help file, by Pico Technology Ltd
Palm Programming by Glen Bachmann, published by SAMS
www.palm.com
NewsGroups
pilot.programmer
pilot.programmer.gcc

Written by Matthew Laver

Western Canada: - Vancouver, B.C. Tel: 1-(604) 925-6150    Fax: 1-(604) 925-6170 Toll Free:1-(800) 663-6001

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