Re: watering system, second attempt.

From: andy (news4_at_earthsong.free-online.co.uk)
Date: 08/08/04 

Date: Sun, 08 Aug 2004 16:29:00 +0100

On Sun, 08 Aug 2004 05:48:18 +0100, andy wrote:

> On Sun, 08 Aug 2004 02:23:50 +0000, Rich Grise wrote:
>
>> andy wrote:
>>>
>>> http://skullcap23.tripod.com/daily-water3-bw.png
>>> http://skullcap23.tripod.com/daily-water3-bw.jpg
>>>
>>> One thing i'm not sure about is whether i need the 2N3906 on the output,
>>> or whether i could drive the MOSFET directly from the 4538 monostable's
>>> outputs if i used the noninverting outputs and put the diodes the other
>>> way round.
>>
>> Keep the 2N3906. It gives a good solid pullup to drive the gate cap. This
>> is what you want, isn't it?
>>
>> And, it looks like it waters either
>> A) by timer
>> B) when you push either button
>
> It waters in the morning when one switch is set high, and in the evening
> when the other one is. Moving the switches does trigger it, but that's a
> side-effect.
>
>> or is there something I'm missing?
>> Is the 4538 just one-to-a-package? If so, you could lose
>> one of them by just oring the switches together. :-)

i don't think that would work anyhow - the 4538 triggers on a rising edge
of the output of the 'or' gate between inputs A and B. This will let you
trigger on either a rising or falling edge, by choosing which input to
connect the trigger signal to and using the other to gate it with. but i
couldn't see any way of triggering on both edges using just one 4538.

> There are two to a DIL package. 

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