How get data from glucometers in J2ME using serial port?

Question

I have to do an application for a GPRS modem JAVA (J2ME) programmable that must interface with an electromedical device (glucometer).

I have an input buffer and an output buffer on the serial port of the device.

When the application starts, I listen on the serial port and I receive from the glucometer one byte with the decimal code "5" which corresponds, to the ASCII table, the symbol of Enquiry and after 15 seconds I get the bytes "4" that corresponds to the End of Transmission.

To receive data from the glucometer I need to send an ACK signal (acknowledge) which corresponds to the byte "6". I tried the following forms:

outBuffer.write("ACK\r\n".getBytes()); //first without setting the charset and after I trying to set all the charset.

I tried to send a byte buffer like this:

byte[] bSend = new byte[] { 6 }; outBuffer.write(bSend); //(I tried also with the byte 10 (LF) and 13 (CR)).

The result is that I can not receive data but I get cyclically but only the values 5 and 4.

With all the software that can comunicate with serial port (like Serial Monitor) if I send an ACK message I receive data from glucometer correctly.

I think my problem is due to the value of the ACK coding in Java, someone can indicate any solution?

fvu fvu · Accepted Answer · 2013-03-11T10:50:13

As this seems to be a pretty low-level interface that uses ASCII control characters to do its communication I think you need to send these byte values verbatim, and without extra stuff like newlines or whatever. This means that

byte[] bSend = new byte[] { 6 }; 
outBuffer.write(bSend);

Is the correct approach. Now, this protocol looks a lot like ASTM E1381, so I checked here and paragraph 6.1.2 might be related to your problem:

When the meter initiates the Establishment Phase, the meter determines if the computer is connected by initially sending an <ENQ> character. If the computer responds within 15 seconds by sending an <ACK> character, the meter proceeds with Data Transfer Mode. If the computer responds within 15 seconds with a <NAK> character, the meter sends an <EOT> then attempts to enter Remote Command Mode, by looking for an <ENQ> character from the computer. Also see "Section 6.2 Remote Command Mode Protocol". Any response within 15 seconds to the meter’s <ENQ> other than an <ACK> or <NAK> character causes the meter to send an <EOT>, delay one second, then send another <ENQ>. If the computer does not respond within 15 seconds, then the meter sends an <EOT>, delays one second, then sends another <ENQ> and waits again for a response from the computer. Note: One second after sending an <ENQ>, the meter may enter a low power mode. Thus, there is a possibility that the first <ACK> sent by the computer is not read correctly. In this case, the meter responds with an <EOT>, delays one second, then sends another <ENQ>.

Emphasis mine, I guess that that's what's happening. So, you should repeat sending another ENQ to get it into data transfer mode, assuming that that's what you want.

How get data from glucometers in J2ME using serial port?

2 Answers