Interfacing an ADC-16 with a Palm Pilot

Introduction

Palm pilots are becoming ever more popular and useful as everyday organisers, but can they be used for datalogging?

Yes is the answer, a Palm Pilot has an RS-232 serial connector so in theory any Pico serial port device can be used in conjunction with a Palm Pilot.There are two main considerations, Hardware & Software.

Hardware

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

Pin	Name	Function
3	TX	Data from the PC to the ADC-16
2	RX	Data from the ADC-16 to the PC
7	RTS	Held at a positive voltage (>7V) to power the ADC-16
5	GND	0V line
4	DTR	Held at a negative voltage (<-7V) to power the ADC-16

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:

Pin	Name	Function
1	DTR	Data Terminal Ready signal
2	VCC	3.3 Volts
3	RD (in)	Receive data
4	RTS (out)	Request to send
5	TD (out)	Transmit data
6	CTS (in)	Clear to send
7	GP1 (in)	Interupt line
8	GP2 (in)	modem sync
9	unused	unused
10	GND	signal ground

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. The device fits in series with the serial cable.

Power adapter

It is recommended that you check this adapter thoroughly once constructed to ensure that no large voltages are fed directly into the Palm Pilot as it could cause damage. The only signals going into the Palm should be the datalines and the ground, not the power lines

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.

static unsigned char channels[] = {0X1F, 0X3F,0X5F,0X7F, 0X9F, 0XBF, 0XDF, 0XFF};

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

msg = channels[0]; SerSend(SerIORef, &msg, StrLen(&msg), &error);

Wait for response

Resolution (bits)	Conversion Time (ms)
8	6.6
9	8.9
10	14
11	23
12	41
13	78
14	151
15	298
16	657

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

The above code uses the orignal serial manager so that the program will function on the older Palm products such as the US Robotics Palm Professional. The program will also function on later models such as the Palm 3, Palm Vx, Palm 3c and Palm M100. For better performance on the newer models there is an improved operating system that has a better serial manager that could be used

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

For information on any of the Pico Technology products in this document please E-mail Pico Technology