LVPK162-12 (LK162-12) does not work with TTL

gmconanplz · Post by **gmconanplz** » Tue Jul 22, 2008 3:37 pm

I am having a LK162-12 powered by 5V battery. I connected the Rx/Tx pins from the 4 pins connector to the tmote sky Tx/Rx pins. Tmote sky operates at 3V.

Then I soldered the zero ohm resistors from RS232 to TTL. Next, I sent the clear command 0x0C from the tmote sky to the LCD. The connection between the tmote and the LCD seemed to work but I can only see a strange character (not even sure if I should call that a character

) on the LCD .

Any idea why the LCD can't understand the command correctly. I set the baud rate, stop bit, parity , etc of the tmote according to the LCD standard. I also repeated the test with different baud rate, different command and it gave me the same character.

When I tested the LCD with PC using RS232 , it worked correctly.

I will appreciate any help. Thank you in advance. Btw, is there an easy way to change the baud rate of the LCD in TTL? Previously, I changed the baud rate by sending the command to it with RS232. However, resoldering to RS232 is really a pain.

Clark · Post by **Clark** » Tue Jul 22, 2008 5:59 pm

Hi Gmconanplz,

I understand you've got a tmote sky device that you're attempting to connect to an LK162-12 unit.

The first thing to note, is that the LK will expect data at TTL levels, meaning Rx and Tx should be operating at 5v. As the tmote is a 3.3v device, and I can't find much to say otherwise in the data sheet, I would guess that the Rx and Tx signals from the unit would be at 3.3v as well.

It is possible to get a voltage translator in between those two devices, something like a Maxim MAX3373E may work.

As for the commands, they'll work the same in TTL as they do in RS232, you'll probably just need a device other than the PC to issue them. As for the protocol jumpers, if you haven't done so already, I'd recommend using solder blobs rather than messing around with those zero ohm resistors.

If you have any further questions regarding that display, just let me know.

Thanks,
~Troy

gmconanplz · Post by **gmconanplz** » Wed Jul 23, 2008 11:25 am

Thank you for your reply. I will try to use the converter.

In the previous post, I mentioned that the LCD printed out the same character. Now I realized that this character is the first one on the Matrix Orbital start-up screen (Look like it is the tail of the ... turtle). Anyway, it is the first character on the start-up screen. Does this make any sense to you?

Also, do you think I messed up the zero ohm resistors?

Thanks

Clark · Post by **Clark** » Wed Jul 23, 2008 4:02 pm

Hi Gmconanplz,

A converter sounds like an excellent idea. Just be sure that your controller is outputting data that makes sense to the display.

The turtle tail does make sense, I had a feeling you were getting a custom character from our start screen. That character is usually sent when the display receives the value 0 from the host. Therefore, I believe some data may be getting through, but it is not being read correctly. You may also want to make sure that the Tx from the tmote is connected to the Rx on the display, and visa versa.

As for the resistors, they should be fine, I just wanted to let you know that if you wanted to , you could get rid of them and use solder to make the connections instead. It might be a little easier to make the switch that way.

~Troy

gmconanplz · Post by **gmconanplz** » Mon Jul 28, 2008 11:27 am

Hi Troy,

I am still waiting for the MAX converter to come. In the mean time, I tried to measure the output from the Tx pin of tmote and the input from the Rx pin of the LCD. They looks identical. My question is, if I use the converter, should the receiver pin have the higher amplitude since it is 5 voltage (tmote is 3.3 voltage).

Another question is can you tell me any LCD that works at 3.3 voltage. I would like to buy one to replace the current LVPK162-12.

Finally, I don't know much about how the hardware UART transmits the byte so this may sound like a stupid question. Please help to clear my head. When I tried to transmit the byte 0x0 continuously , the oscilloscopes displayed 00000000 1 00000000 1 etc. I don't know where this 1 is coming from. When I tried to transmit the byte 0xFF continuously, the oscilloscopes displayed 11111111 0 11111111 0 etc. Again I don't know where this 0 comes from. Finally, when I tried to transmit 0xAA , it gives me 1010101100 1010101100 etc which I expected to be 10101010 10101010 etc. Can someone please explain this to me?

Thanks,

Andy

Clark · Post by **Clark** » Mon Jul 28, 2008 4:21 pm

Hi Andy,

The display will be expecting 5v levels, if the tmote is at 3.3v levels, the higher amplitude belongs on the display side at the Rx pin. If you'd like to receive responses from the display, you'll need a second line connecting the Tx from the display to the Rx on your tmote.

As for the bit patterns you've got there, you should be expecting nine (9) bits on each as the unit expects 8 data bits plus one stop bit. This makes me a little wary of the last bit pattern which has ten. Could be a counting error, a mistype, or the last bit could signify the end of a transmission.

If you're looking for units that communicate natively at 3.3v, you'll be limited to 1U sized screens. These include the new LK204-7T-1U, GLK19264-7T-1U, and the GLK24064-16-1U.

I think that covers things for now, if you've got any further questions, please just post them up here.

Thanks,
~Troy

gmconanplz · Post by **gmconanplz** » Tue Jul 29, 2008 12:21 pm

Hi Troy,

I just have a quick question. Does LVPK162-12 expect a start bit as well? I think my tmote sends out the start bit + 8 bit data + stop bit, which adds up to 10 bits. This could explain why I sent out 10101010 and received 0 (start bit) 01010101 (eight bits data were reversed as the least significant bit is sent out first) 1 (stop bit). When I sent out 0 , I would receive 0 00000000 1 (yesterday I thought it was 8 zeros , but it is actually 9 zeros . Sorry about this). Similarly, when I sent out 0xFF, I would receive 0 11111111 1 .

Thanks,

Andy

Clark · Post by **Clark** » Wed Jul 30, 2008 9:34 am

Hi Andy,

No worries, looks like you've got your tmote output figured out now.

The LK162-12 will expect an 8N1 configuration; 8 data bits, no parity bits, and one stop bit. This means no start bit, and no flow control as well.

~Troy

gmconanplz · Post by **gmconanplz** » Wed Aug 13, 2008 2:13 pm

Hi Troy,

The MAX3373E is so tiny for me to work with. Do you know any other converter with bigger size? I am looking for something to attach to a bread board. It is the best if you can point out some US sellers because it took me almost 2 weeks to order from Maxim. Please help !!!!

Thank you in advance.

Andy

Post by **Henry** » Wed Aug 13, 2008 4:01 pm

gmconanplz wrote:Hi Troy,

The MAX3373E is so tiny for me to work with. Do you know any other converter with bigger size? I am looking for something to attach to a bread board. It is the best if you can point out some US sellers because it took me almost 2 weeks to order from Maxim. Please help !!!!

Thank you in advance.

Andy

I would look for a dip package from digikey, they have a bunch of them.