74HC595 Question
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[font=arial,helvetica]I have been using the '595' with my LED displays and am very happy with it,
mostly ·that means I actually got it to work [noparse]:)[/noparse]. I am now considering using a
'595' to control a bank of relays. My question(s) are:
If i use more then 1 HC595 will the 8bit stream cycle the first 595 on its
way to the 2nd 595? I notice that my display has a flicker to it. Its really
slight but I wonder if that might cause problems with a relay bank.
How far is it safe to operate a HC595 from a BS2? Should I follow the same
rules as for RS232? I would like to have my relays up to 12 feet away.
All ideas are appreciated,
[/font]
mostly ·that means I actually got it to work [noparse]:)[/noparse]. I am now considering using a
'595' to control a bank of relays. My question(s) are:
If i use more then 1 HC595 will the 8bit stream cycle the first 595 on its
way to the 2nd 595? I notice that my display has a flicker to it. Its really
slight but I wonder if that might cause problems with a relay bank.
How far is it safe to operate a HC595 from a BS2? Should I follow the same
rules as for RS232? I would like to have my relays up to 12 feet away.
All ideas are appreciated,
[/font]
Comments
I've been using a 595 too. I think there's a QH' output which can be connected to the input of the following 595. Of course you need 16 clock pulses to transfer 16 bits of data thru the 2 ICs.
I'm currently experiencing with the 74HC165, which is a parallel in - serial out shift register. I need 2 of it to get 16 inputs. I'll let you know the results of this experience.
Best regards,
Phil.
Original Message
From: electronguy@aol.com
To: basicstamps@egroups.com
Sent: Monday, December 25, 2000 11:12 PM
Subject: [noparse][[/noparse]basicstamps] 74HC595 Question
[font=arial,helvetica]I have been using the '595' with my LED displays and am very happy with it,
mostly ·that means I actually got it to work [noparse]:)[/noparse]. I am now considering using a
'595' to control a bank of relays. My question(s) are:
If i use more then 1 HC595 will the 8bit stream cycle the first 595 on its
way to the 2nd 595? I notice that my display has a flicker to it. Its really
slight but I wonder if that might cause problems with a relay bank.
How far is it safe to operate a HC595 from a BS2? Should I follow the same
rules as for RS232? I would like to have my relays up to 12 feet away.
All ideas are appreciated,
[/font]
>I have been using the '595' with my LED displays and am very happy with it,
>mostly that means I actually got it to work [noparse]:)[/noparse]. I am now considering using a
>'595' to control a bank of relays. My question(s) are:
>
>If i use more then 1 HC595 will the 8bit stream cycle the first 595 on its
>way to the 2nd 595? I notice that my display has a flicker to it. Its really
>slight but I wonder if that might cause problems with a relay bank.
>
>How far is it safe to operate a HC595 from a BS2? Should I follow the same
>rules as for RS232? I would like to have my relays up to 12 feet away.
>
>All ideas are appreciated,
How are you driving pin RCLK? Normally, you send out the proper number of
clock pulses to shift all the bits into the shift registers, then send a
pulse out to RCLK to latch the data into the output latches. Note that you
can cascade as many shift registers as you need by connecting the Qs output
from the previous shift register to the data input of the next shift
register. Requires a total of 3 pins from the processor.
You can reduce that to 2 pins if you can tolerate some update latency and
extra parts. The HC595 does NOT have schmitt trigger inputs, which is a
hassle. You couple the data line to the RCLK buss via a long RC
delay. Because the HC595 requires fast edges on the clock inputs, you have
to follow that RC delay with a schmitt trigger. The idea is to always keep
the data line in one particular state, changing it briefly just before
sending out a clock pulse, then returning the data line back to the idle
state. When all the serial clock pulses have been sent, you hold the data
line in the opposite state for a period longer than the RC delay.
Note that the TPIC series of shift registers DO include schmitt triggers
and thus all you need to implement a 2 wire interface is a RC delay (1
resistor, 1 capacitor).
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
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