Questions on decoder and 7 segment display.

[forder]

Hi, I'm new here and I have some in my current project, I'm working on displaying two 2-digit values, which are the temperature from two different sensors. Each value is encoded into 8 bit binary number. So before the data goes through the RF transmitter, the encoder will produce 16 bits output, which is the total of the two 8-bit values. The 16 bits ouput will be transmitted via RF link. My part starts from the RF receiver until the display of the values (displayed in 7 segment). The RF receiver will receive 16 bits, where the first 8 bit are the value of the first temperature and the last 8 bit is the value of the second temperature. But from the RF receiver point of view, it is still just a 16 bit information. My question is how do I separate them back into two 8-bit information? Is there a chip that I can use? Another question is, suppose I have separated the 16 bit information into two 8-bit information, how do I display one 8-bit information on two 7-segment LED display, since the 8 bit information is the value of the temperature (which contains two digit, so it needs two 7 segment LED display). I know how to drive a 7-segment display if it is a 4-bit information (by using SN74LS47 or any BCD-to-7segment decoder), which also only require one 7-segment display. But I'm bit lost when it comes to 8 bit with two 7 segments. Note that I am not permitted to use any micro controllers, PLD or any programmable device. Hints or suggestions are really appreciated.

 

[ericgibbs]

Hi,
>> Displaying two 2-digit values, which are the temperature from two different sensors.
Each value is encoded into 8 bit binary number.
So before the data goes through the RF transmitter, the encoder will produce 16 bits output,
which is the total of the two 8-bit values.
The 16 bits ouput will be transmitted via RF link.
My part starts from the RF receiver until the display of the values (displayed in 7 segment).
The RF receiver will receive 16 bits, where the first 8 bit are the value of the first temperature and the last 8 bit is the value of the second temperature.
But from the RF receiver point of view, it is still just a 16 bit information.
My question is how do I separate them back into two 8-bit information? Is there a chip that I can use?

You could use a 2 * 8 bit shift registers, load the bits serially and then read the four separate bytes.

Another question is, suppose I have separated the 16 bit information into two 8-bit information, how do I display one 8-bit information on two 7-segment LED display,since the 8 bit information is the value of the temperature (which contains two digit, so it needs two 7 segment LED display).
You say the a single tempr is 8 bit binary, as you know 8 bits can have a decimal value of 0 thru 255 so, if you want to display the value as decimal you need 3 * 7 seg displays. for each temperature.
The problem is you have to convert the 8 bit binary into 3 * BCD before using 74LS47, the 74LS47 will not work correctly with binary inputs.
This conversion can be a problem area.

I know how to drive a 7-segment display if it is a 4-bit information (by using SN74LS47 or any BCD-to-7segment decoder), which also only require one 7-segment display.
But I'm bit lost when it comes to 8 bit with two 7 segments.
Note that I am not permitted to use any micro controllers, PLD or any programmable device.

Does this help

 

[ThermalRunaway]

I have a question to ask before I can give you my suggestion. Regarding the 16-bit data, I understand this is made up of the information from two temperature sensors and you need to split it up into two sets of 8-bit data so that it can be processed by two seperate display circuits.

Is the 8-bit data RAW data from the temperature sensor? In other words, do the full 8-bits of the data represent the temperature or are there some start / stop bits involved as well?

If the full 8-bits represents the temperature then my idea is down the pan - that's why I needed to ask you this question first

Brian

 

[forder]

The 8 bit data represents the temperature sensor.. or at least that is how I understand how the process runs.. the guy who works on sending the data told me that his RF transmitter will send 16 bit data to my RF receiver, which contains two 8-bit temperature values.

Another thing is, the display will only show only two digits of the temperature values, which means the maximum value it can display is 99 degree.. if it reaches more than 99 degree, the display will not show any number (the observer then understands that the temperature has reached its maximum limit).

 

[ericgibbs]

The 8 bit data represents the temperature sensor.. or at least that is how I understand how the process runs.. the guy who works on sending the data told me that his RF transmitter will send 16 bit data to my RF receiver, which contains two 8-bit temperature values.

Another thing is, the display will only show only two digits of the temperature values, which means the maximum value it can display is 99 degree.. if it reaches more than 99 degree, the display will not show any number (the observer then understands that the temperature has reached its maximum limit).

hi,
Understood, but if the 2*8 bit data is binary, that where its gets difficult [ without a PIC] to do a 8 bit binary to a 2 digit BCD, for the display drivers.

Are you SURE the 8 bit data is in Binary? OR is it maybe Packed BCD, ie the high nibble is 4 bit BCD and the low nibble 4 bit BCD, this way is quite common?

 

[forder]

i'm sorry.. i'm not really sure whether packed BCD or binary.. if you don't mind, can u give me the solutions for both cases? or if you have other suggestions, i would really appreciate it.. thanks

 

[ericgibbs]

i'm sorry.. i'm not really sure whether packed BCD or binary.. if you don't mind, can u give me the solutions for both cases? or if you have other suggestions, i would really appreciate it.. thanks

hi,
If its packed BCD ie: two BCD nibbles/byte and you have two bytes ie: 16 bits, use a 2*8 shift register.
Serial input to the SR, with parallel output, when the data in the SR is steady strobe it into two 7447 LED decoder drivers.

If its Binary I would suggest you use a PIC to to do the binary to bcd conversion and also drive the LED's.
If you try the binary to bcd conversion using discrete logic it can become big and messy.
Thats techno-speak for don't do it that way.

If you Google for the discrete method you see what I mean.

Hope this helps.