could anyone explain how this circuit work ?

Thread Starter

bebo

Joined Aug 29, 2019
4
Hi All,

I'm trying to know how the staircase timer read the 220 ac signal when a push button pressed.

i bought one staircase timer and before i install it i open it and draw the schematic for button signal.

here is the timer

timer.png

The schematic which i draw from timer pcb.

WhatsApp Image 2019-08-29 at 4.11.21 PM.jpeg

WhatsApp Image 2019-08-22 at 4.23.49 PM.jpeg

could anyone help me to understand how this circuit work ?

Regards :)
 

cmartinez

Joined Jan 17, 2007
6,789
That can't be right ... the voltage breakdown of the 1N4002 is given as 100V according to its datasheet... that spells trouble ... Plus, I honestly fail to see what the 15K and 1N4007 are doing in that configuration, other than generating heat. Are you sure the diagram you drew is the same as what's physically present in the circuit?

upload_2019-8-29_11-1-49.png
 

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Tonyr1084

Joined Sep 24, 2015
4,180
Either it's a transistor or a voltage regulator I'm seeing in the pictures but am not seeing anything like it on the schematic. Something's missing.

I also see three caps but only one shown in the drawing. Two push buttons AND A REALLY BIG SEVEN SEGMENT DISPLAY. Where are those? And how is the display driven?

I say again, something's missing.

I'm impressed that the fusible link has been soldered. I've never had success soldering a fusible link. I always blow them out before I get a chance to power the board. Not impossible, just something I've never been able to do.
 
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Thread Starter

bebo

Joined Aug 29, 2019
4
hi,

i only drew schematic for interfacing 220v button with the mcu of the timer ,because i don't know how it works .
all diods in the schematic 1n4007 :)

other components for
power rectification & regulation(diodes+7805+caps)
light control(relay and its driver circuit)
segments for displaying the time
buzzer and its driver
buttons for setting the time and manual control for the lamp.
screw terminals(blue for 220/12v transformer in/out///green for (Line/nutral/lamp/buttons).

Note:usually in our buildings the buttons used in the stair has an indicator neon lamps in parallel with the button terminals.
i dont know if this affect on the circuit design.

bell-push-button-with-indicator-345.jpg
 

LesJones

Joined Jan 8, 2017
2,511
Now that you have given some more details about the use the timer is designed for the circuit makes more sense. Until you provided the information in post #8 I could not see the purpose of the 15K resistor and the diode in series with it. The neon (Plus current limiting resistor.) in the switch will be directly across it's contacts. As there will be a number of these switches in parallel the current would be large enough to trigger the opto isolator and the current limited by the 100K resistor in series with the opto isolator input would be so low that the neons would be very dim. The 15K resistor will provide the required current for the neons without the opto isolator being triggered. If the resistor and capacitor were not connected to the output of the opto isolator it's output would be a string of pulses at the mains frequency. the capacitor filters out these pulses so you get a dc voltage while the switch is pressed. This signal triggers the timer. If you want to know how the timer part works you will have to trace out that part of the schematic and post it.

Les.
 

Thread Starter

bebo

Joined Aug 29, 2019
4
Now that you have given some more details about the use the timer is designed for the circuit makes more sense. Until you provided the information in post #8 I could not see the purpose of the 15K resistor and the diode in series with it. The neon (Plus current limiting resistor.) in the switch will be directly across it's contacts. As there will be a number of these switches in parallel the current would be large enough to trigger the opto isolator and the current limited by the 100K resistor in series with the opto isolator input would be so low that the neons would be very dim. The 15K resistor will provide the required current for the neons without the opto isolator being triggered. If the resistor and capacitor were not connected to the output of the opto isolator it's output would be a string of pulses at the mains frequency. the capacitor filters out these pulses so you get a dc voltage while the switch is pressed. This signal triggers the timer. If you want to know how the timer part works you will have to trace out that part of the schematic and post it.

Les.
thank you,your effort is appreciated .
i only want to understand how can i interface the 220v buttons with Microcontroller :)

as i understand the number of buttons (have indicator lamps ) are limited ?
if yes,how to calculate the max number of buttons without triggering the opto isolator?

Regards
 

cmartinez

Joined Jan 17, 2007
6,789
i only want to understand how can i interface the 220v buttons with Microcontroller :)
If that's the case, I can help you with that. But there would also be some additional programming involved (or additional electronics on the low side of the optoisolator) because 220VAC would be intermittently activating the opto at a mains frequency (60 or 50 Hz, depending where you are)
 

Thread Starter

bebo

Joined Aug 29, 2019
4
If that's the case, I can help you with that. But there would also be some additional programming involved (or additional electronics on the low side of the optoisolator) because 220VAC would be intermittently activating the opto at a mains frequency (60 or 50 Hz, depending where you are)

i have good programming skills with arduino and some pic microcontrollers :)
but my electronics skills simple :v

as i see in les post the resistor and capacitor ensure a dc voltage while activating the opto .
is there another components to be added before connect the output to mcu ?


also is there a better and more efficient circuit do the same function considering the indicator lamps ?

thanks in advanced
 

LesJones

Joined Jan 8, 2017
2,511
I don't think there is a way to calculate the maximum number of buttons with the information you have. You could probably get some idea by finding the value or the resistor in series with the neon in each switch. You could then work out the total current for all the neons in parallel. You would then have to measure the minimum voltage that triggered the timer input. from that you work out the current that would be required to give that voltage across the 15K resistor. I would then say the maximum number of switches that you could would be the number that added up to about half that value. To eliminate that problem you could wire a neutral to all the switch boxes to provide the current for all the neons. This assumes that there is a third connection in the switches to wire them in this way.
With you limited knowledge should you be doing the wiring in a public building ?

Les.
 

cmartinez

Joined Jan 17, 2007
6,789
There you go. Here's a circuit that will deliver 60Hz pulses at its output when connected to a 220 VAC RMS mains.

R1,R2,R3,R4,R9 and R10 can be thought of as a single 28.2K resistor, the reason there are six 4k7 in series (instead of a single one) is to help dissipate heat easier without using a single high power resistor. This way you can use the easy to find 1/2W resistors, instead of a single bigger and costlier 28.2K 2W resistor. That's what the blue trace in the graph is showing.

R5, along with the R1,R2,R3,R4,R9 and R10 array, make a voltage divider, to which the 4N25 input is connected. This way, the 4N25 input never sees a voltage above ±3.2V at its input. This because, according to its datasheet, the input is rated with a maximum reverse voltage of 6V.

As you can see, pulses of up to 7mA go through its input, which is well within safe and operational limits.

R8 is there to make the sim work, it would be nonexistent in a real circuit. R6 is also nonexistent and is there to measure the current flowing through the input of 4N25, this because that particular model in LTspice won't allow that sort of measurement directly.

upload_2019-8-30_17-7-10.png
 

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MisterBill2

Joined Jan 23, 2018
5,228
The circuit drawing is missing quite a few of the components that show in the poor photo. So there is no point in attempting a description of how the circuit works because it is not what actually is there.
FIRST, provide a good photo that shows all of the parts clearly. Use enough light so that they are not in shadows. Then trace out the complete circuit, and it is likely that how it works can be explained.
 

cmartinez

Joined Jan 17, 2007
6,789
The circuit drawing is missing quite a few of the components that show in the poor photo. So there is no point in attempting a description of how the circuit works because it is not what actually is there.
FIRST, provide a good photo that shows all of the parts clearly. Use enough light so that they are not in shadows. Then trace out the complete circuit, and it is likely that how it works can be explained.
Check this statement by the TS in post #10:

i only want to understand how can i interface the 220v buttons with Microcontroller :)
 

MisterBill2

Joined Jan 23, 2018
5,228
OK, I did not read through all of the posts because it certainly appeared, after the first 2 or 5 that nobody else had realized that the circuit presented in the first post did not reflect what the actual hardware was. Sorry about being a bit impatient, but it really is bothersome to get questions asking for answers when most of the data needed to give an adequate answer is left out. This past week has been that sort of week out in the real world, at least for me.
 

Tonyr1084

Joined Sep 24, 2015
4,180
it certainly appeared, after the first 2 or 5 that nobody else had realized that the circuit presented in the first post did not reflect what the actual hardware was.
IN post #5 I pointed out that there was a lot missing from the drawing to the photos.
Either it's a transistor or a voltage regulator I'm seeing in the pictures but am not seeing anything like it on the schematic. Something's missing.

I also see three caps but only one shown in the drawing. Two push buttons AND A REALLY BIG SEVEN SEGMENT DISPLAY. Where are those? And how is the display driven?

I say again, something's missing.
 

MisterBill2

Joined Jan 23, 2018
5,228
Asking "how a circuit works" is generally taken to mean the circuit shown as a system. More information in the first post would have pointed things in a different direction.
AND, if you are wanting to use the buttons to interface with a microprocessor there is no need to get the 220 volts circuit involved, because the processor already has a correct voltage source for it's operating voltage. In addition, that source already has adequate isolation from all the noise on the 220 volt power circuit.
But if you want the simplest isolation circuit, it uses a neon bulb, a series resistor to limit the current, and a photo-transistor to sense the light. Such an arrangement can easily have 10KV isolation. AND you can build it your self.
 
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