Faster Finger Circuit - Doesn't work - Where did I go wrong?

KaiL
Member • Jul 4, 2011

Faster Finger Circuit - Doesn't work - Where did I go wrong?

This is the diagram of my circuit

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Circuit Operation
J1 is normally closed unless used for Reset
J1 J2 and J3 are Switches

Faster Finger Circuit Operation:
When J2 is turned on first , LED1 will turn on and even if J3 is turned On later, LED2 will not turn on at all.

Problem:
However ,when J2 is turned on first , LED1 is turned on but when I turn on J3 later , LED2 also turn on. It is the same result even if I turn on J3 first.

Please help me by pointing out my error. Thanks.😀

Replies

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Replies

silk smita

Member • Jul 4, 2011

First of all make neat connections in any type of simulation software.
sometimes overlapping of two wires and wrong connections occurs because of this reason.

according to me you can modify your connection where R2 is placed.otherwise your circuit is seemed to be OK.

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KaiL

Member • Jul 5, 2011

silk smita
First of all make neat connections in any type of simulation software.
sometimes overlapping of two wires and wrong connections occurs because of this reason.

according to me you can modify your connection where R2 is placed.otherwise your circuit is seemed to be OK.
OK I will do that.😀

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KaiL

Member • Jul 5, 2011

I just try modify the connection where R2 is placed but still can't achieve the result I want. Could anyone give me some more idea how I can achieve the result I want?

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Ramani Aswath

Member • Jul 10, 2011

KaiL
I just try modify the connection where R2 is placed but still can't achieve the result I want. Could anyone give me some more idea how I can achieve the result I want?
I think that R1 and R2 are acting as a voltage divider. Ideally this junction should be at ground potential for preventing the gate of the second SCR from firing. In this circuit R1 being 200 Ohms and R2 being 1K there is enough voltage at the junction to fire the SCR even when J2 is on. why do you need R2 at all? Try without it or interchange R1 and R2.

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KaiL

Member • Jul 10, 2011

bioramani
I think that R1 and R2 are acting as a voltage divider. Ideally this junction should be at ground potential for preventing the gate of the second SCR from firing. In this circuit R1 being 200 Ohms and R2 being 1K there is enough voltage at the junction to fire the SCR even when J2 is on. why do you need R2 at all? Try without it or interchange R1 and R2.
I tried interchange the value of R1 and R2 but still it doesn't work and when I remove R2. LED will still light up.(J2 on first LED1 on and J3 on later LED2 also turns on)

Did I mess out in any area in this circuit? For R1 and R2? or other parts?

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Ramani Aswath

Member • Jul 10, 2011

KaiL
I tried interchange the value of R1 and R2 but still it doesn't work and when I remove R2. LED will still light up.(J2 on first LED1 on and J3 on later LED2 also turns on)

Did I mess out in any area in this circuit? For R1 and R2? or other parts?
What purpose does D4 serve? Can be removed I think. A Zener diode in series with J3 should help.

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KaiL

Member • Jul 10, 2011

bioramani
What purpose does D4 serve? Can be removed I think. A Zener diode in series with J3 should help.
From what my lecturer said , he said that the diode is to prevent the switch at J3 from trigger the SCR when you pressed J2 first. It is the same when you press J3 first and it will prevent the SCR from triggering when you turn on the switch at J2. However , it doesn't work for some reason.

By the way , what does Zenor diode do when you connect it in series with J3?

I followed what you said by connecting Zenor diode in series.
This is what happened.
When the Zenor diode is in series with J3 , it works when J2 is turned on first and LED1 turns on and when J3 is turned on later , LED2 will not turn on. However , when I pressed the master reset at J1 and I do it by turning on J3 first , LED2 turns on and when J2 is turned on later , LED1 also turns on.

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Ramani Aswath

Member • Jul 10, 2011

KaiL
From what my lecturer said , he said that the diode is to prevent the switch at J3 from trigger the SCR when you pressed J2 first. It is the same when you press J3 first and it will prevent the SCR from triggering when you turn on the switch at J2. However , it doesn't work for some reason.

By the way , what does Zenor diode do when you connect it in series with J3?

MCR 22 has a very low gate trigger current of 30 micro amps. Even a small voltage can cause triggering. The circuit shown in your diagram can easily supply this. Can you please tell what exactly you want the circuit to do?

I followed what you said by connecting Zenor diode in series.
This is what happened.
When the Zenor diode is in series with J3 , it works when J2 is turned on first and LED1 turns on and when J3 is turned on later , LED2 will not turn on. However , when I pressed the master reset at J1 and I do it by turning on J3 first , LED2 turns on and when J2 is turned on later , LED1 also turns on.
MCR-22 has a gate trigger current as low as 30 micro amps. The circuit shown in your diagram can easily trigger D3. I did not fully get what you want the circuit to do. Can yougive this info again? We have to ensure that the voltage at J3 is less than 0.1 V when LED 1 is on.
You want LED 1 only should be on if J2 is pressed first and LED2 should not come on even if J3 is activated subsequently and LED 2 only should be on if J3 is pressed first and LED1 should not come on even if J2 is activated subsequently. Is this what you want?

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KaiL

Member • Jul 11, 2011

bioramani
MCR-22 has a gate trigger current as low as 30 micro amps. The circuit shown in your diagram can easily trigger D3. I did not fully get what you want the circuit to do. Can yougive this info again? We have to ensure that the voltage at J3 is less than 0.1 V when LED 1 is on.
You want LED 1 only should be on if J2 is pressed first and LED2 should not come on even if J3 is activated subsequently and LED 2 only should be on if J3 is pressed first and LED1 should not come on even if J2 is activated subsequently. Is this what you want?
Ya that is what I want for my circuit.
Isn't MCR-22-6 has a trigger current of 200 micro amps at Max and Gate trigger Voltage at 0.8V at Max? Based on the datasheet that I found on the web - #-Link-Snipped-#

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Ramani Aswath

Member • Jul 11, 2011

Why not look at the whole circuit again? What you need to do is to disable the gate of SCR 2 when SCR1 is on first and vice versa. You are also using very low value resistors. Please check out this circuit.
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When SW1 is pressed SCR 1 comes on as does LED1. At the same time the potential at A drops to ground (actually the combined forward drops of LED1 and SCR1). If SW2 is now pressed the gate of SCR 2 cannot be triggered. If SW2 is pressed first the reverse happens. The zeners are used as insurance to prevent random triggering caused by variations in the forward drops of the components.

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KaiL

Member • Jul 13, 2011

bioramani
Why not look at the whole circuit again? What you need to do is to disable the gate of SCR 2 when SCR1 is on first and vice versa. You are also using very low value resistors. Please check out this circuit.
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When SW1 is pressed SCR 1 comes on as does LED1. At the same time the potential at A drops to ground (actually the combined forward drops of LED1 and SCR1). If SW2 is now pressed the gate of SCR 2 cannot be triggered. If SW2 is pressed first the reverse happens. The zeners are used as insurance to prevent random triggering caused by variations in the forward drops of the components.
Thanks again for your help😁

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KaiL

Member • Jul 14, 2011

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Hi again. I have tried the circuit that you have come up using MultiSim but it doesn't work at all.

Could you explain to me how you get the Value for R2 and R4 (10K ohms) , R1 and R3 (1k Ohms) and why do you choose a 6.2 Volt Zener Diode???

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Ramani Aswath

Member • Jul 15, 2011

KaiL
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Hi again. I have tried the circuit that you have come up using MultiSim but it doesn't work at all.

Could you explain to me how you get the Value for R2 and R4 (10K ohms) , R1 and R3 (1k Ohms) and why do you choose a 6.2 Volt Zener Diode???
It is a simple exclusive 'OR' circuit. The switches J2 and J3 should both be Normally Open push button type. Your circuit shows J2 as an NC. Why? This will automatically switch LED1 on every time after J1 is reset.
With 18V supply the LEDs can get about 15 milliamps, which should be ample. The 10K in the gate limits gate current to abou 1 milli amp, which is high enough to trigger the chosen SCR.

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KaiL

Member • Jul 16, 2011

Could I check with you why the value of gate current is about 1 milli amp? Isn't the value of gate current at Max is 0.2 milli amp based on this Datasheet? or did I read it wrongly?
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Ramani Aswath

Member • Jul 16, 2011

You are right. However, with 200 ohms and 18 v you were passing a much higher current. I just reduced the current to 1 ma. You can increase the resistance to 50 k ohms and still be OK.
By the way, how is the circuit panning out? I do not have the components immediately to hand. Otherwise I would have checked it out by now.

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KaiL

Member • Jul 17, 2011

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Thanks again for your help.

Maybe I have calculated wrongly somewhere in my circuit. Either the value of R1 or R2 which is why it doesn't work the way I want it to go when I combine everything together?

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Ramani Aswath

Member • Jul 18, 2011

I still feel that you will be better off not using a voltage divider for the gate trigger. The circuit I had given with Zeners should work. Since your source is 18v to get 0.2ma you have to use a resistor 18/.2= 90 K Ohms. This should go directly to the gate through a momentary on switch. That is, R2=90kOhms and no R1. J2 must be N/O with a momentary on function. The mistake is in taking 0.8V as your source voltage. You must remember that it is the gate current that triggers and not the voltage. However, the gate junction requires a minimum of 0.8V to allow 200 micro amps to pass. This can be safely ignored as you have a much higher 18V source. The voltage at point C is irrelevant.

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KaiL

Member • Jul 21, 2011

bioramani
I still feel that you will be better off not using a voltage divider for the gate trigger. The circuit I had given with Zeners should work. Since your source is 18v to get 0.2ma you have to use a resistor 18/.2= 90 K Ohms. This should go directly to the gate through a momentary on switch. That is, R2=90kOhms and no R1. J2 must be N/O with a momentary on function. The mistake is in taking 0.8V as your source voltage. You must remember that it is the gate current that triggers and not the voltage. However, the gate junction requires a minimum of 0.8V to allow 200 micro amps to pass. This can be safely ignored as you have a much higher 18V source. The voltage at point C is irrelevant.
I see. Thanks for your help again.😁😁😁

By the way , could you tell me how you choose the Zener Diode of 6.2V and not other value?

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Ramani Aswath

Member • Jul 25, 2011

KaiL
I see. Thanks for your help again.😁😁😁

By the way , could you tell me how you choose the Zener Diode of 6.2V and not other value?
I am not an electronics person. Way back in 1970 we were building some process control circuits. IC circuits for voltage stabiliztion were not easily available. 6.2 V zeners have the best stability with ambient temperature variation because of the breakdown junction characteristics. We used a lot of these zeners then.
It was just by habit that I suggested that voltage. You can use any zener with a voltage above 3 volts for this purpose. 6.2 V is not a calculated requirement. All that is needed is that it should block the combined forward drop of the LED and the SCR in the triggered condition.

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KaiL

Member • Jul 25, 2011

I see. Thanks

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KaiL

Member • Jul 26, 2011

Hi again. Could you assist me with one problem? My circuit supply current is about 1.51 Ampere and I am wondering how kind of wires I can use? I need to solder everything onto the copper stripboard but I have no idea what kind of wires which are able to withstand 1.51 Ampere. If possible , could you help me at this website <a href="https://sg.element14.com/" target="_blank" rel="nofollow noopener noreferrer">element14 Singapore | Electronic Components Distributor | Premier Farnell Group</a> and show me the wires that is available for me.

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Ramani Aswath

Member • Jul 27, 2011

KaiL
Hi again. Could you assist me with one problem? My circuit supply current is about 1.51 Ampere and I am wondering how kind of wires I can use? I need to solder everything onto the copper stripboard but I have no idea what kind of wires which are able to withstand 1.51 Ampere. If possible , could you help me at this website <a href="https://sg.element14.com/" target="_blank" rel="nofollow noopener noreferrer">element14 Singapore | Electronic Components Distributor | Premier Farnell Group</a> and show me the wires that is available for me.
1.51 Amps is small. Any hook up wire should work. Try a 0.5 mm[SUP]2 [/SUP]conductor.
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keerthi92

Member • Jul 27, 2011

hey guys sry i did not know where ask abt my doubts.....can sum1 pls help me out?

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KaiL

Member • Jul 27, 2011

bioramani
1.51 Amps is small. Any hook up wire should work. Try a 0.5 mm[SUP]2 [/SUP]conductor.
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So does this wire work for me?
WIRE, TRI RATED, ORANGE, 0.5MM, 100M

Reel Length (Imperial):328ft; Reel Length (Metric):100m; Conductor Area CSA:0.5mmÂ²; Jacket Colour:Orange; Jacket Material😛VC (Polyvinyl Chloride); Conductor Material:Copper; Externa

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Ramani Aswath

Member • Jul 27, 2011

KaiL
So does this wire work for me?
WIRE, TRI RATED, ORANGE, 0.5MM, 100M

Reel Length (Imperial):328ft; Reel Length (Metric):100m; Conductor Area CSA:0.5mm²; Jacket Colour:Orange; Jacket Material😛VC (Polyvinyl Chloride); Conductor Material:Copper; Externa
That should work.
Do you not have any electronic hobby shop where you can buy small lengths such wires?

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KaiL

Member • Jul 28, 2011

bioramani
That should work.
Do you not have any electronic hobby shop where you can buy small lengths such wires?
Not really.

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KaiL

Member • Aug 3, 2011

KaiL
Not really.
my bad I write reply wrongly. it should be yes

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