Re: Light sensitive relay switch alternative?

On Sun, 24 Jul 2005 19:02:56 GMT, Kristian Ukkonen
<kristian.ukkonen@xxxxxx> wrote:

>
>Andy Turner wrote:
>> On Sun, 24 Jul 2005 15:42:52 GMT, Kristian Ukkonen
>>>Andy Turner wrote:
>>>>Well sorta.. the problem is with the switch implementing a "delay
>>>>circuit to avoid cycling", which I guess I should have spotted when
>>>>ordering it.. So this means that it's simply not fast enough for the
>>>>application. I presume the delay is implemented in the chip so there'd
>>>>be nothing I could do about removing it? Or does the capacitor do the
>>>>delay (smaller capacitor, smaller delay?).
>>>
>>>Yes, make the capacitor at + input of opamp smaller
>>>for a smaller delay.
>> Cheers! I've noticed that it takes longer to switch one way than back
>> again. Also, I notice that there's two capacitors, one 100uf and one
>> 470uf. Is this implementing the two different delays? What would
>> happen if I took the capacitors off and just wired direct? Would that
>> give me no delay or would it stop working or blow something?
>
>Do notice: "CAPACITOR AT + INPUT OF OPAMP"
>
>The other capacitors, according to circuit diagram at
>the webpage selling the circuit, are just for powersupply.
>http://www.maplin.co.uk/Media/product_pdfs/qp97.pdf

Ah! Ok, cheers.


>
>> I apologise for not knowing too much about what must be GCSE level
>> electronics. I do very much regret opting for a different subject at
>> school..!
>
>Schools are just for realizing that by reading books
>you can find out ANY information. For learning electronics,
>find a book on electronics, read it and start doing stuff.
>You can test circuits with free switcher cad 3 download:
>http://ltspice.linear.com/software/swcadiii.exe
>Most simple electronics, like this circuit, are very easy
>to design - it is just resistive voltage dividers and basic
>stuff like that.

OK, I'm gonna play with that. I do want to learn this stuff and with
an actual project to push me into learning it, it should be the
motivation I need.



>One resistive divider, 100k potentiometer, gives the
>comparator switch level to - input.
>
>Another resistive divider 150k, VDR, 15k gives the
>other voltage. There is, in addition, a "delay" circuit
>by the 17k and 180k resistors, diode and 100uF capasitor.
>
>When LDR has high resistance (dark), voltage is high and the
>100uF capacitor charges slowly to this high voltage (and some
>current goes through 100k but to simplify forget this now).
>When LDR resistance drops (light), diode prevents the lower
>voltage from charging the capasitor, and capasitor discharges
>through the 100k resistor until eventually voltage is
>lower than the voltage set by the 100k potentiometer, and
>the state of the relay changes.
>
>Now, when LDR again has high resistance (dark), the 100uF
>cap is starting to charge and voltage eventually becomes
>higher than the voltage from 100k pot, and the state of
>relay changes again.
>
>The opamp (the triangle part with inputs marked "-" and
>"+" is a comparator - it compares whether - or + input
>has a higher voltage, and changes output accordingly.
>
>LDR = light dependant resistor
>
>I hope this helps you understand how the circuit works.
>You can enter the circuit to switcher cad 3, and replace
>LDR with a switch.. See how it works!

Thanks for that. I kinda understand it, but only in that way where you
understand what someone's saying, but you couldn't write it yourself
(if you see what I mean!). I'll play with that software and perhaps
figure out for myself what changes I want to make. At least any
mistakes won't result in real damage or mishaps!


>To answer your original question: Only the 100uF capacitor
>matters for the delay. Take it away and you have no delay.
>I'd suggest setting a little delay. Simulate the circuit
>with Switcher cad 3, and find out correct size for cap!!

I'll do that, thanks. And I appreciate your help with the bigger
picture, rather than just telling me what to do, but helping me figure
it out for myself. Teach a man to fish and all that...


Thanks again.


andyt

.