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need help on design of mcu avr based gate opner circuit

sherazi

Mar 8, 2010
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design ideas regarding circuit board design for a sliding gate opner.
for the following

1) power supply design... 230-12v+24v 1.5A
2) input isolation using opto couplers
3) ac motor speed control
4) how to use moc3022 for motr triacs... why in most circuits is the anode conected to vcc... if connected how can i controll it to be on off
5) using pots for reading user input for different variables such as delays for closing gate
 

saurabh17g

Mar 8, 2010
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1) power supply design :
do it using ic 723.
http://www.national.com/mpf/LM/LM723.html#Overview
u might require current boosters in the form of transistors.
for dual power supply, design 2 pss and tie one's + to other's -
U can use 78xx/LM 317 series as well.
Be particular regarding transformer selection. Cost and size depends heavily on current requirement.
 

sherazi

Mar 8, 2010
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i have solved out considerable amount of problems...

now can any 1 help in the method and code for triac based speed control.. triac being interfaced to avr using moc 3022...
 

(*steve*)

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Generally the solution involves tracking the zero crossings of the mains and either delaying the turn on of the triac until part way through each half cycle, or allowing every n'th half cycle through (n is usually odd). The method you use depends on your load.
 

sherazi

Mar 8, 2010
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if i use a dual power supply of 12 and 24 v how can i detect the zero crossing...


any specific reason for odd n?
 

(*steve*)

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sorry, I was expecting the motor would be running from the mains. Using triacs on a DC motor will not be effective.
 

sherazi

Mar 8, 2010
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the motr runs from mains... its ac motor... power supply is for the microcontroller... i wanted to ask that ho van i make the microcontroller detect the zero crossings...

further more when u siad
or allowing every n'th half cycle through (n is usually odd).

whats the reason for odd n
 

(*steve*)

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OK, it depends on the motor you are trying to control. Resqueline has provided more info on this in another thread I think. Odd n means that you get alternating positive and negative half cycles.

Googling yeilds a number of circuits that can be used to detect zero crossings. They fall into one of 2 categories, those that generate a pulse at the zero crossing point, and those that change state at the zero crossing point. The choice is up to you.
 

sherazi

Mar 8, 2010
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ok ... now i got it.... i think if iam using an ac motor of low wattage then i can even use the on -off controll... without the zerocrossing consideration... but keep the interval such that the motor recieves alternate + and neg cycles
 

saurabh17g

Mar 8, 2010
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go through this
http://www.st.com/stonline/books/pdf/docs/11796.pdf

page no 27- zero crossing interrupt is mentioned

just to confirm,
zero crossing is the event during which the AC mains wave crosses zero, rite?
if that is so, u have to start a timer and generate a wave to control gate.
I just went through the document hurriedly. This was the thing that i understood.
 
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