Reading Clock Pulses of a Master Clock with Arduino.

A

Adriaan&CO

New Member
Greetings all,

i need a circuit to detect positive and negative pulses with an Arduino.
the inputvoltage can be 12v, 24v and 60v.
i had come up with the circuit in the picture, and that is working but the input resistor is getting awfully Hot til it burns.
i have to put in a 10 Watt resistor and it is still getting real hot.
Does anyone has an idea for a circuit to do this without the use of the Resistor getting real Hot.

Greetings Adriaan
 
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Why are you using such a low value resistor (360 ohm)?, is there a specific need for it to be so low?, and you're also causing a LOT of heat in the zener diodes.

I presume this is for testing the pulses for a synchronised clock, as in an old school?.
 
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Correct Old school Central Clock system.

i want to modernize it and build some digital display showing the time,
with an Arduino and some Large 7 seg displays.

the resistor is calculated, but even when i use a 10K resistor of 10 Watt it is getting realy hot.

Greetings Adriaan
 
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Calculated from what?, and what is the voltage applied to it?.
 
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I'm pretty sure I know what you are talking about, but to be safe (and prevent 20 needless posts) please post a sketch of the input waveform with peak amplitudes and timing.

ak
 
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1. Other than for lightning protection, I don't see any explicit reason for the zener diodes.

2. The 6N137 is way overkill for this application.

Based on the 6N137 datasheet, its transfer curve indicates reliable operation at 2 mA input current. Design the circuit for this current when the input is 12 V. This will yield an input current of less than 12 mA at 60 V, still within the part's normal operating range.

With an LED forward voltage of 1.5 V at low currents, Ohm's Law says the input current limiting resistor should be 5.25K. Rounding that down to 5.1K:

Input current at 12 V: 2.06 mA
Input resistor power: 21.6 mW

Input current at 60 V: 11.5 mA
Input resistor power: 0.67 W

At 60 V, a resistor rated for 2 W will get warm but not hot.

NOTE: The power ratings above are for *continuous* conduction at the stated voltages. If the input waveform spends significant time at 0 V, the actual power dissipation will be much lower.

ak
 
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Also -

Which resistor is overheating, R5 or R18?

There is no GND or return current path for the input signal, so I don't see how anything does anything.

ak
 
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AnalogKid said:
I'm pretty sure I know what you are talking about, but to be safe (and prevent 20 needless posts) please post a sketch of the input waveform with peak amplitudes and timing.

ak
Click to expand...
The first scope picture is the clock running in 1:9 mode ( fast mode so the image could be made )
the second picture is the clock running in fast forward mode, this system is 24V, but we also have 60v systems running.
 

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The Idea of the zeners is to stabelize the voltage over the opto to ensure it is not above the nominal voltage of the 6n137

the 6n137 is used to opto isolate the circuit from the +24v and -24 volt of the supplying clock signal.

Adriaan
 
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