Mikebits

I have not looked at the datasheet for the HEF part, but the 74HC/HCT237 part is simply the 138 part with a latch added. Here is verbage from the datasheet.

The 74HC/HCT237 are 3-to-8 line decoder/demultiplexers
with latches at the three address inputs (An). The “237”
essentially combines the 3-to-8 decoder function with a
3-bit storage latch. When the latch is enabled (LE = LOW),
the “237” acts as a 3-to-8 active LOW decoder. When the
latch enable (LE) goes from LOW-to-HIGH, the last data
present at the inputs before this transition, is stored in the
latches. Further address changes are ignored as long as
LE remains HIGH.
So tie your OE1 low, your OE0 high, use one pport pin as a write for the LE pin.
Sequence of events:

• On pport output address
• Assert latch En low --Keep address pins valid at this point.
• deassert LE --make LE high
• address is now saved

Here is a link to a TI part.
http://focus.ti.com/lit/ds/symlink/cd74hct237.pdf

My only thinking is that my approach will waste 1 pin for the LE line. Maybe someone has a better solution. I will have to think on it a bit.

Eric, I never heard of HEF parts, is that like fast logic?

Mikebits

I think, if you use Extended pport mode, you can use a control port pin for LE, that way you still have 8 data pins.

Interfacing to the IBM-PC Parallel Printer Port

ericgibbs

hi menticol,
The 74HC237 only latches the input address, not the output state.
If a new address is applied to the input and the LE switched the addressed output will change.

All this means thats once latched the addressed output will not change until the next address is latched LE.
This would normally be used on a address 'bus' that was being shared by other ic's.
The LE would enable the 237 to hold the address.

If you look at the paraport diagram, you have 12 output lines.

Can you post a diagram showing exactly what you want to do with the logic.?

Might be able to suggest alternatives.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Mikebits

I kinda thought that is what he wanted to do. If I am mistaken, my apologies.
Your right though, a block diagram or something would help.

ericgibbs

hi Mikebits,
I think a drawing would help us both to figure out a solution.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Menticol

Ok I have made a diagram, I hope its correct



The thing consists of a parallel port, 74LS139, a "X" circuit for each 74LS139 output, and its respective relay.

The "X" circuit and relay should change its state when receiving the pulse from the 74LS139, and keep it while the 74LS139 actuates other "X" circuits

If I try to use the schematic without the "x" circuit, I'll be able to turn on only 1 device at time, so would be a controller with limited utility

__________________
La Rotta

If you are those who adds new features or appearance to everything around, and take the limited budget to the limit, this blog is for you (spanish)

ericgibbs

hi menticol,
The circuit you have posted, the 139 will not 'hold' the output state.
As soon as you load another address the 'old' 'X' will drop out.

EDIT:
Look at this option, each 139 controls, 4 latches.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Menticol

Hello again Eric and Mikebits!

Sorry by the delay, my job is killing all my electronics time

Thank you by your suggestion Eric, but I'm afraid it gets too expensive vs. benefit. Each latch consumes 2 pins of the decoder, so I'm gonna need a lot of cascaded decoders and latches to control a respectable ammount of devices.

I'm been studing the diagram of my 20th june post, about cascading the decoders. I understand more decoders means more A. B, C inputs, and the free pin of the second decoder is used to feed an eventual third decoder, and so on. But I cannot figure out yet.

I have found an interesting dual flip flop circuit, but multipling it times x numer of decoders, no way (even using a hex 74LS174 flip flop, stills require too much adtional components) Anyway I leave it here if anyone could find it useful.

About the LM35 interface through MCP3202, I'm very interested on it, but I don't wanna be rude (like the newbies that invade the site) asking you to do my work, so if you would like to share some clues to make my own schematic, I'll be grateful

Thank you by the EPP idea Mikebits, I'll read more about it, I would use it as a B plan if the decoder idea sinks.

edit: I found the MCP3202 datasheet! I was mispelling the name... but no typical aplication or test circuit

Attached Images

flipflop.JPG (24.5 KB, 4 views)

__________________
La Rotta

If you are those who adds new features or appearance to everything around, and take the limited budget to the limit, this blog is for you (spanish)

ericgibbs

hi,
This is the inteface I use with the PC parallel port.

If you are savvy with Visual Basic, let me know if you need the VB5 program, I will pretty it up and post it.

You can get the MCP datasheet from DatasheetArchive :: Free Datasheet Search Engine :: Electronic Components

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

ericgibbs

hi menticol,

For latches look at the HEF4724 datasheet

Its a addressable 8 bit latch, that holds the state of the output, until over written.


HEF4724 Selling Leads,HEF4724,PHILIPS*[Philips Semiconductors] Datasheet PDF

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Menticol

Program exchange would be great!

Here is my program, its a simplified drawing of my room (without the dirty clothes and dirt under the bed, offcourse!). Touching the objects sends a signal trough parallel port, turning the thing ON or OFF. Based on inpout32.dll code, found on planet-source-code. Nothing complex.

My last "high technology" advance was adding a dimmer I've found abandoned on my university. The pot was broken, so I wired a resistor to it. When the relay is open, the dimmer's pot resistance is 0 so the room lights shine with full intensity. When the relay is closed, wires the dimmer through the resistor, so the light fades down. With a simle VB mp3 player, the light can be dimmed automatically if some music starts (a geek way to entertain female guests, but may be improved... maybe a solenoid driving the fireplace? hahahaha)

Attached Images

deltacontrol.JPG (105.5 KB, 5 views)

__________________
La Rotta

If you are those who adds new features or appearance to everything around, and take the limited budget to the limit, this blog is for you (spanish)

ericgibbs

hi,
A couple of years ago I played around with voice control using the PC and the microsoft speech programs linked into VB.

Using the parallel port.

I could command the PC to play classical, pop music,etc, next track, mute, volume up/down [activeX component]. Control the TV channels, lights etc.
That was cool.

It was the lack of female guests that gave me a problem.

Look at the microsoft site for voice/speech control

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Menticol

Hahaha yes! Making the PC speech is great, but never tried speech recognition (you're on the great leagues!). By the way, If you wanna equip your programs with a beautiful female voice, check this out

AT&T Labs Text-to-Speech: Demo

EDIT: They lowered the voice quality since last time I played with it but you still get the idea

__________________
La Rotta

If you are those who adds new features or appearance to everything around, and take the limited budget to the limit, this blog is for you (spanish)

ericgibbs

hi Menticol,
Attached zip file is for:

LM35 temperature sensors driving a MC3202 dual 12bit ADC, using Visual Basic5, connected to the PC using the parallel port.

Included is a circuit diagram, the VB5 program source code also the *.exe.

Its a complete package for building and running the project.

Anyone requiring more information, please ask.

EDIT: Added a screen shot.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

rainbow

hi all
i have a problem with the parallel port ( exactly with status pins)

i implement an adc using (dac , comparator and a simple software of succusive approximation)
i use an lm741 as a comparator with 12v-ground.
when comparator is high output=9.8v
when comparator is low output=1.89v
this output must be connected to status through parallel port
comparator is either high or low, the status pin don t change its output,it has an output of 4.7v (for only one pin of course ).
is this because of low power from my circuit?
my circuit could not change the pin votage???
when i have connected the ground of the circuit tothis pin it changed to low
but it dont response to my comparator (lm741).......
what is my fault ....?? please it is important for my project

hint:sorry if my english is bad or there is some errors