Below is a two digit Binary to BCD converter using counters.
The binary number is initially loaded into the two left binary down counters.
It then counts down while the two right BCD counters simultaneously count up from zero.
When the binary counters reach zero and stop, the BCD value is contained in the two BCD counters.
This value can then be latched into the BCD to 7-segment IC for display.

For a three-digit count you would add another BCD counter.

As you can see, it involves a fair amount of circuitry, requiring 6 chips for three digits, not counting the clock.

 

As you can see, it involves a fair amount of circuitry, requiring 5 chips, not counting the clock.

6+ chips, as he needs 3 BCD digits for 255, so another BCD counter....

 

6+ chips, as he needs 3 BCD digits for 255, so another BCD counter....

Yes, I amended my post to reflect that.

 

The constraint of my project is no microcontroller at all.

What are the learning objectives of this project? Hopefully it's not to figure out how to convert an 8 bit binary number to BCD...

 

Yes, I amended my post to reflect that.

Strange, I'm seeing the revised text but the earlier graphic?

 

omg the converter looks very difficult, since I haven't learnt counter yet.. Actually the learning objective is applying the knowledge that have learnt in designing instrumentation system. In my case, I chose to design like digital thermometer without any microcontroller. Because the ADC that have been learnt is 0809, so I think I have to convert the binary output to somewhat that can be fed to 7 segment. Then, minimal I can display the 0 to 255 result then convert again to get the voltage on LM35...


But after this discussion, I realized that my plan is inefficient at all. Or I pick wrongproblem statement.....

 

You can just use a row of 8 LEDs to output the binary value of your ADC.

 

But after this discussion, I realized that my plan is inefficient at all. Or I pick wrongproblem statement.....

There is a 74185 component in Proteus, but it won't run in the simulator. The datasheet shows an 8 bit converter requiring 3 of the chips. My logic gate implementation took over 120 gates.

 

There is a 74185 component in Proteus, but it won't run in the simulator. The datasheet shows an 8 bit converter requiring 3 of the chips. My logic gate implementation took over 120 gates.

The 74185 was an OTP ROM programmed to convert 6bit binary to 1 and a half BCD digits. I say 'was' because you cannot buy them from anywhere now except Chuang Ming's emporium on AliExpress (best of luck on that one).

 

The 74185 was an OTP ROM programmed to convert 6bit binary to 1 and a half BCD digits. I say 'was' because you cannot buy them from anywhere now except Chuang Ming's emporium on AliExpress (best of luck on that one).

What you need is a ROM chip containing 256 bytes x 10 bits. Since you are more likely to find chips with 8-bit wide memory, what you need are two chips of 256 bytes x 8 bits ROM, such as Signetics 82S114N. Then you will have to learn to program the ROM.

It is still easier to use an MCU and no other ICs required.

 

Strange, I'm seeing the revised text but the earlier graphic?

Yes, I didn't change the graphic.
I should have made that clear.

 

After some reading, I try to do the display with IC 7107 (in Proteus). From digital voltmeter circuit in Google, I can display 28.5 Volt input as 28.4 Volt output in 7segment. There is 0.1 difference. Is it normal? How can I improve the accuracy?
Another question is, what is EPROM? Is it microcontroller?

If I choose EPROM to display the resulting voltage from sensor, how can I place units, tens, or hundreds?


Below is my 7107 circuit, whichis same with voltmeter

 

If I choose EPROM to display the resulting voltage from sensor, how can I place units, tens, or hundreds?

If you use a 16 bit wide EPROM, it's a straightforward look up table.

 

Im sorry, what is look up table?

 

Im sorry, what is look up table?

It's just a table. Might also be spelled lookup table.

For a binary to BCD table, address 0x10 would be programmed with 0b0001 0110. Address 0x20 would be 0b0011 0010.

EDIT: corrected typo

 

Here is a simple explanation of a lookup table.

A lookup table is an array of values. Given an address or location, you go to that address and get the contents or stored value.

For example, suppose you have a 4-bit address (0-15) and you want do display two BCD digits:

Address Contents
0000 0000 0000
0001 0000 0001
0010 0000 0010
0011 0000 0011
0100 0000 0100
0101 0000 0101
0110 0000 0110
0111 0000 0111
1000 0000 1000
1001 0000 1001
1010 0001 0000
1011 0001 0001
1100 0001 0010
1101 0001 0011
1110 0001 0100
1111 0001 0101

This is exactly what a SN74185 binary-to-BCD converter does.
This is exactly what you would enter into and EPROM or MCU solution except you would extend this to 8-bit address and 2-4-4 bit output. In the case of an MCU solution you can choose to multiplex 4-bits to a 7447 or you can multiplex 7 bits directly to the 7-segment LED displays.

 

After some reading, I try to do the display with IC 7107 (in Proteus). From digital voltmeter circuit in Google, I can display 28.5 Volt input as 28.4 Volt output in 7segment. There is 0.1 difference. Is it normal? How can I improve the accuracy?
Another question is, what is EPROM? Is it microcontroller?

If I choose EPROM to display the resulting voltage from sensor, how can I place units, tens, or hundreds?


Below is my 7107 circuit, whichis same with voltmeter

View attachment 236999

Its showing the correct value that you've asked it to show... the fault isn't in the device, its the way you're using it. Read the datasheet.