Demultiplexer - Page 2 - Electronic Circuits Projects Diagrams Free

nobtiba · 3rd May 2007, 06:26 PM

By saying "either on or off" I mean at first I want to ouput high level then after that turn to low level (or vice versa). What if I want to get the values stored in latch or if I don't care about these values?

Today I checked the stored again with more options but I can not find any 4-to-16 decoder (checked: MM74hc4514, CD4514BE, HEF4514). So at last I have to buy 2 ICs 74LS138 which are the 3-to-8 decoders to check how it work. If everything is ok, then I will buy more. But I have a question, even if I have alot of 74LS138, what is the maximum number of output I can get (control buy parallel port as discussed). I need more than a hundred but I am afraid I could get only about 64 (8x8=64) ?

nobtiba · 4th May 2007, 03:33 AM

By saying "either on or off" I mean I want the output to be high level after that turn to low level (or vice versa).
What if I do not care about the values stored in the latch or if I want to output it?

Yesterday I searched again all the electronic shops but I could not find any 4-to-16 decoder (searched: HEF4514,HC4514,CD4514). Do you think any type may be easier to find?

Eventually I have to bought 2 ICs 74LS138 which are 3-to-8 decoder. What will be the maximum number I can get (control by parallel port like above discussed) ? I guess only 64 (8x8=64) but I really need about more than a hundred of output. Do you think I can get it by 74LS138 ?

ericgibbs · 4th May 2007, 07:49 AM

hi,
If you decode all 8 output bits on the parallel port you can get 0 to 255 individual lines.
By using latches on the 8bit output and using other pins on the port you could get more than 255, if required.

The 138 as you know is a 3 to 8 decoder, it has other control pins on the input side of the ic, as well as the 3 address pins.
The problem is the 'selected' output is active LOW. Also you will require many 138s to decode 128 or 256 lines.

Its important to remember the 'selected' outputs are NOT latched,
as soon as you select another output [LOW] the previous output will revert to a HIGH state.

Can you post a diagram of the 'simple' version you are going to test, with a description of what you want the outputs for???

Are you able to buy HEF4067's ?

nobtiba · 4th May 2007, 01:58 PM

But HEF4067 is for analog right? I will post my circuit a bit later, after my dinner and a few more tests, I'm testing it on the whiteboard and it works but I don't understand how could I have 255 output as you said !?

ericgibbs · 5th May 2007, 09:17 AM

hi nobtiba,
Yes, the 4067 is an analog decoder, but if pin #1, 'Z' is connected to '0v' then the 'selected' output is LOW, if pin#1 is +V, then 'selected' output is HIGH. So they can be used as 4514/4515's. [4067 is more expensive IIRC]

With Ref to the LS138 3 to 8, look at Nigels earlier post on how this is done.

>> don't understand how could I have 255 output as you said !?

If you decode ALL 8 output lines, you will get 255.

If you only want 127, decode 7 output lines.

ericgibbs · 5th May 2007, 01:39 PM

hi nobtiba,

Attached rough drawing a 138 decoder version.

As the parallel port is driving 16 * 138 ic's, you may require a buffer driver on the D0 to D2 and D6 port pins.

REMEMBER: the 'selected' channel be be LOW and revert back to a HIGH when deselected.

nobtiba · 7th May 2007, 07:22 AM

Thank you Eric,

Your support is great! I really appreciate it.
My test circuit works as I hope. Unfortunately, after all, I realize that the decoder may not the right thing as I hope. When I said outputs I mean we can set whatever combination of values. But here, with the decoder (whatever type) only the 'selected' pin is 'set' which mean only one pin can be effected. For example: if I have a 3-to-8 decoder, I can not set the output (let's say: from pin 0 to pin 7) to: HHLHLLHL (H: High, L: Low), so it is not the same as parallel pins which has this capability!!
I really do not know any method that could help me to do this ?? The parallel port is good, I can set what ever group of bits to the output. The only limittation is the number of pins (8 pins) but I need about more than a hundred.
All the method I know to expand the output, until now, is only help me to set one 'selected pin' not ANY group of pins.
Do you know any solution ?

ericgibbs · 7th May 2007, 08:37 AM

hi nobtiba,

The other way I can suggest is this.

Retain the first set of decoders that drive the second group, but have their inputs latched. [ideal ic would be 4514/4515]
This 1st group is enabled by using another output pin from the port. From memory there are 4 more output pins?

Call it address or data select control.

The second group of LS138's are replaced by octal latches, the 1st 138 outputs select the individual octal latches.

The address/data pin is set to 'data', now output the 8 bit wide data pattern [on the same 8 pins as you did the address]
and strobe that 8 bit data into the octal latches.

I hope you can follow the general idea?

nobtiba · 7th May 2007, 09:13 AM

I spent time reading your instruction. But not very sure that I understand it clearly.

My final target is: Having about 100 (or more) pins (called pin 1 to pin 100) which could satisfy:

- First, set all to high level : HHHHHH....HHH (100 high)
- Now want to set pin 2,3, 45, 68 to high: then I have: LHHLLLL....LLH(45)LLLL...LH(68)LL..L
- Then I set pin 1,3,7,38 to High, I have : HLHLLLHLL....LLH(38)LLLL..LLL

some thing like that, in which H and L stand for High and Low logic level output at the pins.

ericgibbs · 7th May 2007, 09:53 AM

hi
This should give you the outputs you require.

Consider 8 outputs from the port as 8 bit Address or Data.

Set the Addr/Data line so that you write the Address of the Latch you want to write to.

Strobe the Addr into the Decoder latches.

Set the Addr/Data line to DATA.

Write an 8 bit Data byte to the selected 8 bit Latch.

Strobe the Data into the latches. and repeat as required.

You will require a 'image' byte in your PC program for each Latch, update the 'image' and output it.

I have only drawn as a block diagram, you will have to configure the logic with ic's you can get.

Its drawn to show ALL 255 bits, reduce it to suit your application.

Is this any clearer?

nobtiba · 7th May 2007, 10:16 AM

It is very intuitive!
Tomorrow I will go to buy new ICs. The ICs here is really expensive, so that I would like to ask for your recommend to eliminate unneccessary redundancy. Here, hard to find any 4-to-18 decoder.

So for my application I need 128 output (parallelly). Here is my temporary list:

1) 3-to-8 decoder 74LS138 ( how many ? - I got one now)
2) 8 bit latch -> don't know what type is suitable?

is this enough?

I am not very familiar with "latch" and "strobe" concept. I heard that with the latch it is not really parallel which means not every output at the same time !? My application really ask for exactly all at the same time !

ericgibbs · 7th May 2007, 12:54 PM

hi,
Can you get any of these ic's.

74174
74237
74259
74273
74373
74374
74573
EDIT: 74100
Can you say why you want to control 100+ output bits?

nobtiba · 7th May 2007, 02:51 PM

I will check it tomorrow, this time all the shops closed already. So if I could get one of the following:74100,74174,74237,74259,74273,74373,7437 4,74573 then it will be ok right ?
I want to control 100 + output bits because I need to make other wires of other devices to connect to /then/ separate from the grown. But this control should be at the same time and the values High or Low (1 or 0) is decided freely.
Could you tell me what is the function of the above ICs and how will I use them ?

ericgibbs · 7th May 2007, 03:08 PM

hi,
I would recommend that you download the datasheets for the devices listed and study their function.

Its important that you do not waste your money buying the wrong ic's.

The ones I have listed are data latches.

www.datasheetarchive.com

http://www.hanssummers.com/electronics/datasheets/

EDIT:
>> I need to make other wires of other devices to connect to /then/ separate from the grown. [ground???]

Do these other wires have any voltages on them?, also are they able to accept the TTL HIGH [+5Vdc]

nobtiba · 7th May 2007, 05:46 PM

They do nothave voltages on them, they could accept TTL High I guess, at least I tested with 3.4 Volt and everything is still ok.

However, I still fell that the system could not give me any combination of bit as I want. For example with parallel port I could output the combination like: 10011101 but with 3-to-8 decoder I could only set ONE 'selected' pin.

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3rd May 2007, 06:26 PM	(permalink)
nobtiba	By saying "either on or off" I mean at first I want to ouput high level then after that turn to low level (or vice versa). What if I want to get the values stored in latch or if I don't care about these values? Today I checked the stored again with more options but I can not find any 4-to-16 decoder (checked: MM74hc4514, CD4514BE, HEF4514). So at last I have to buy 2 ICs 74LS138 which are the 3-to-8 decoders to check how it work. If everything is ok, then I will buy more. But I have a question, even if I have alot of 74LS138, what is the maximum number of output I can get (control buy parallel port as discussed). I need more than a hundred but I am afraid I could get only about 64 (8x8=64) ?

4th May 2007, 03:33 AM	(permalink)
nobtiba	By saying "either on or off" I mean I want the output to be high level after that turn to low level (or vice versa). What if I do not care about the values stored in the latch or if I want to output it? Yesterday I searched again all the electronic shops but I could not find any 4-to-16 decoder (searched: HEF4514,HC4514,CD4514). Do you think any type may be easier to find? Eventually I have to bought 2 ICs 74LS138 which are 3-to-8 decoder. What will be the maximum number I can get (control by parallel port like above discussed) ? I guess only 64 (8x8=64) but I really need about more than a hundred of output. Do you think I can get it by 74LS138 ?

4th May 2007, 07:49 AM	(permalink)
ericgibbs	hi, If you decode all 8 output bits on the parallel port you can get 0 to 255 individual lines. By using latches on the 8bit output and using other pins on the port you could get more than 255, if required. The 138 as you know is a 3 to 8 decoder, it has other control pins on the input side of the ic, as well as the 3 address pins. The problem is the 'selected' output is active LOW. Also you will require many 138s to decode 128 or 256 lines. Its important to remember the 'selected' outputs are NOT latched, as soon as you select another output [LOW] the previous output will revert to a HIGH state. Can you post a diagram of the 'simple' version you are going to test, with a description of what you want the outputs for??? Are you able to buy HEF4067's ? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

4th May 2007, 01:58 PM	(permalink)
nobtiba	But HEF4067 is for analog right? I will post my circuit a bit later, after my dinner and a few more tests, I'm testing it on the whiteboard and it works but I don't understand how could I have 255 output as you said !?

5th May 2007, 09:17 AM	(permalink)
ericgibbs	hi nobtiba, Yes, the 4067 is an analog decoder, but if pin #1, 'Z' is connected to '0v' then the 'selected' output is LOW, if pin#1 is +V, then 'selected' output is HIGH. So they can be used as 4514/4515's. [4067 is more expensive IIRC] With Ref to the LS138 3 to 8, look at Nigels earlier post on how this is done. >> don't understand how could I have 255 output as you said !? If you decode ALL 8 output lines, you will get 255. If you only want 127, decode 7 output lines. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

5th May 2007, 01:39 PM	(permalink)
ericgibbs	hi nobtiba, Attached rough drawing a 138 decoder version. As the parallel port is driving 16 * 138 ic's, you may require a buffer driver on the D0 to D2 and D6 port pins. REMEMBER: the 'selected' channel be be LOW and revert back to a HIGH when deselected. __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 12:20 PM.

7th May 2007, 07:22 AM	(permalink)
nobtiba	Thank you Eric, Your support is great! I really appreciate it. My test circuit works as I hope. Unfortunately, after all, I realize that the decoder may not the right thing as I hope. When I said outputs I mean we can set whatever combination of values. But here, with the decoder (whatever type) only the 'selected' pin is 'set' which mean only one pin can be effected. For example: if I have a 3-to-8 decoder, I can not set the output (let's say: from pin 0 to pin 7) to: HHLHLLHL (H: High, L: Low), so it is not the same as parallel pins which has this capability!! I really do not know any method that could help me to do this ?? The parallel port is good, I can set what ever group of bits to the output. The only limittation is the number of pins (8 pins) but I need about more than a hundred. All the method I know to expand the output, until now, is only help me to set one 'selected pin' not ANY group of pins. Do you know any solution ? Last edited by nobtiba; 7th May 2007 at 07:30 AM.

7th May 2007, 08:37 AM	(permalink)
ericgibbs	hi nobtiba, The other way I can suggest is this. Retain the first set of decoders that drive the second group, but have their inputs latched. [ideal ic would be 4514/4515] This 1st group is enabled by using another output pin from the port. From memory there are 4 more output pins? Call it address or data select control. The second group of LS138's are replaced by octal latches, the 1st 138 outputs select the individual octal latches. The address/data pin is set to 'data', now output the 8 bit wide data pattern [on the same 8 pins as you did the address] and strobe that 8 bit data into the octal latches. I hope you can follow the general idea? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

7th May 2007, 09:13 AM	(permalink)
nobtiba	I spent time reading your instruction. But not very sure that I understand it clearly. My final target is: Having about 100 (or more) pins (called pin 1 to pin 100) which could satisfy: - First, set all to high level : HHHHHH....HHH (100 high) - Now want to set pin 2,3, 45, 68 to high: then I have: LHHLLLL....LLH(45)LLLL...LH(68)LL..L - Then I set pin 1,3,7,38 to High, I have : HLHLLLHLL....LLH(38)LLLL..LLL some thing like that, in which H and L stand for High and Low logic level output at the pins. Last edited by nobtiba; 7th May 2007 at 09:22 AM.

7th May 2007, 09:53 AM	(permalink)
ericgibbs	hi This should give you the outputs you require. Consider 8 outputs from the port as 8 bit Address or Data. Set the Addr/Data line so that you write the Address of the Latch you want to write to. Strobe the Addr into the Decoder latches. Set the Addr/Data line to DATA. Write an 8 bit Data byte to the selected 8 bit Latch. Strobe the Data into the latches. and repeat as required. You will require a 'image' byte in your PC program for each Latch, update the 'image' and output it. I have only drawn as a block diagram, you will have to configure the logic with ic's you can get. Its drawn to show ALL 255 bits, reduce it to suit your application. Is this any clearer? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 12:20 PM.

7th May 2007, 10:16 AM	(permalink)
nobtiba	It is very intuitive! Tomorrow I will go to buy new ICs. The ICs here is really expensive, so that I would like to ask for your recommend to eliminate unneccessary redundancy. Here, hard to find any 4-to-18 decoder. So for my application I need 128 output (parallelly). Here is my temporary list: 1) 3-to-8 decoder 74LS138 ( how many ? - I got one now) 2) 8 bit latch -> don't know what type is suitable? is this enough? I am not very familiar with "latch" and "strobe" concept. I heard that with the latch it is not really parallel which means not every output at the same time !? My application really ask for exactly all at the same time !

7th May 2007, 12:54 PM	(permalink)
ericgibbs	hi, Can you get any of these ic's. 74174 74237 74259 74273 74373 74374 74573 EDIT: 74100 Can you say why you want to control 100+ output bits? __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th May 2007 at 01:19 PM.

7th May 2007, 02:51 PM	(permalink)
nobtiba	I will check it tomorrow, this time all the shops closed already. So if I could get one of the following:74100,74174,74237,74259,74273,74373,7437 4,74573 then it will be ok right ? I want to control 100 + output bits because I need to make other wires of other devices to connect to /then/ separate from the grown. But this control should be at the same time and the values High or Low (1 or 0) is decided freely. Could you tell me what is the function of the above ICs and how will I use them ?

7th May 2007, 03:08 PM	(permalink)
ericgibbs	hi, I would recommend that you download the datasheets for the devices listed and study their function. Its important that you do not waste your money buying the wrong ic's. The ones I have listed are data latches. www.datasheetarchive.com http://www.hanssummers.com/electronics/datasheets/ EDIT: >> I need to make other wires of other devices to connect to /then/ separate from the grown. [ground???] Do these other wires have any voltages on them?, also are they able to accept the TTL HIGH [+5Vdc] __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th May 2007 at 04:15 PM.

7th May 2007, 05:46 PM	(permalink)
nobtiba	They do nothave voltages on them, they could accept TTL High I guess, at least I tested with 3.4 Volt and everything is still ok. However, I still fell that the system could not give me any combination of bit as I want. For example with parallel port I could output the combination like: 10011101 but with 3-to-8 decoder I could only set ONE 'selected' pin.