Alt-BEAM Archive
Message #02682
To: mike vidal greenears@yahoo.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 27 Apr 1999 09:59:22 +0200 (CEST)
Subject: [alt-beam] Re: renewed BEAMer
On Mon, 26 Apr 1999, mike vidal wrote:
> - first at the local radio shack they have 74hct14 hex inverting
> schmitt triggers, are these usable in place of the recommended 74c14?
Briefly:
74HC: cmos input switching levels 30% of Vcc and 70% of Vcc;
typical treshold 50% of Vcc. Supply: 2 to 6V
74HCT: TTL input switching levels 0.8V and 2V. Supply: 4.5 to 5.5V
74AC: Basically similar to 74HC, but much higher sink and source
output currents possible. Also higher current consumption in linear
mode (input halfway between 0 and 1), a bit trickier in terms of pcb
layout and decoupling, more expensive and harder to find.
74C: Supply: 3 to 15V, making this a rather different kettle of
fish. Cmos switching levels 30 and 70% of Vcc.
Check the datasheets for more information; they are on the Web.
The best family for BEAM-type designs in general is probably 74HC.
At low frequencies, this family can be made to work at Vcc below
1V, and will retain state (memory, if you will) at something like
0.5V or even less. The outputs will sink and source enough to
handle the base current needed by driver transistors capable of
dealing with any motor you want to use for a small, mobile `bot.
Even 74AC outputs tend to get overloaded if you drive a motor
directly.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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