Re: Substituting a 74HCT74 for a 4013

From: Chris W (1qazse4_at_cox.net)
Date: 03/27/05 

Date: Sat, 26 Mar 2005 23:27:55 -0600

John Fields wrote:

>On Sat, 26 Mar 2005 18:29:17 -0600, Chris W <1qazse4@cox.net> wrote:
>
>
>
>>Can someone tell me how I could use a 74HCT74 in place of the 4013 in
>>this circuit...
>>http://www.uoguelph.ca/~antoon/gadgets/rc-sw.htm
>>
>>I tried adding a pull up resistor to both sets and the second reset.
>>Then I ran the first Q output into one of the inverters on a 7404, with
>>the capacitor to ground and then the output of the inverter into the
>>first reset but it still doesn't seem to be working. Any ideas? I
>>really don't know what I am doing here. Oh and I just need the high or
>>low output, I don't need the TMOS FET.
>>
>>
>
>--- ___ _____
>The HC74 needs a logic low asserted on the SET and RESET inputs in
>order to make them work, while the 4013 needs a logic high to do the
>same thing. Therefore, if you want to substitute an HC74 for a 4013,
>you'll need to invert the signals driving SET and RESET on the 4013.
>
>
>
I guess I wasn't clear, but that is what I am trying to do. After more
checking, I think the inverter I have isn't working right. With no
connections the inputs all read 1.6v and it takes a resistor no larger
than 100 ohms to take pull it down below .1v. Having a resistor in
there is obviously going to interferer with my capacitor charging.
Shouldn't the capacitor pull an input down to 0 volts or is this thing
defective? The markings on the chip say DM7404N. 

-- 
Chris W
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