Alt-BEAM Archive
Message #02067
To: "'beam@corp.sgi.com'" beam@corp.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Tue, 6 Apr 1999 19:32:01 -0700
Subject: [alt-beam] Re: Bicore using 74xx240
Hello David,
The 74LS240 can not (easily) be used for bicore oscillator circuits and
certainly not with 1M resistors. In addition, check your circuit which
appears to have a design problem. As shown, it is the circuit for a 2Nv
"grounded resistor" bicore but in that case you should use a 74HC14. The
more popular "suspended" bicore often uses the 74HC/HCT/AC/ACT240 (and not
LS/ALS/F/S) and replaces the 2 grounded resistors with a single high value
"floating" resistor between the 2 inputs.
regards
Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> -----Original Message-----
> From: David [SMTP:David@quidan.demon.co.uk]
> Sent: Tuesday, April 06, 1999 11:31 AM
> To: beam@corp.sgi.com
> Subject: Bicore using 74xx240
>
> I've tried again to make a bicore out of a 74LS240 and it just won't
> work.
> What's more is that if I use unequal resistors the two LED's do
> pulse, but one faster than the other, using equal resistors the LED's
> do not pulse.
> Here is the circuit diagram I am using, I wonder if you can help me
> out:
>
>
> ____________________________
> | __________________________|__
> | | | |
> | | |\ | |
> | -||--o---------| >o--------o- |
> | | |/ |
> | l |
> | | | |
> | | | |
> | T |
> | | |
> | -o- GND |
> | |
> | |\ |
> ---||--o---------| >o-----------o-----
> | |/
> l
> | |
> | |
> T
> |
> -o- GND
>
>
> All of the enables are connected to GND. The resistors are 1M
> and the capacitors are all .22uF.
>
> --
> David Welch
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