Converting from 30V to 5V or less
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Posted by on September 19, 2008, 9:15 am
Please log in for more thread options I'm using a computer to gather data using LPT1 port. The input pins of the lpt accept 0-5V. I want to know when three utility motors using 30V start and when they end. When a motor starts it gets 30V. Actually they should get 24V but occasional bursts to 30V are normal. The motors themself can handle the extra voltage. What is the simplest way lower the voltage to 5V for my LPT port? I've done simple electronics but a simple schematic would be great. I want to know when each of the motors start. | ||||||||||||||||||||||||||||||||||
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Posted by John Fields on September 19, 2008, 1:23 pm
Please log in for more thread options On Fri, 19 Sep 2008 16:15:13 +0300, spam_filter@invalid.nil wrote: >30V are normal. The motors themself can handle the extra voltage.
> >What is the simplest way lower the voltage to 5V for my LPT port? I've done >simple electronics but a simple schematic would be great. I want to know when >each of the motors start. --- View in Courier: 1/2 WATT 30V----+--[1000]--+------>4.7V
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[MOTOR] [1N5230B] | | GND>---+----------+------>GND
JF | ||||||||||||||||||||||||||||||||||
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Posted by Stephen J. Rush on September 19, 2008, 2:14 pm
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On Fri, 19 Sep 2008 16:15:13 +0300, spam_filter wrote: > I'm using a computer to gather data using LPT1 port. The input pins of
> the lpt accept 0-5V. > > I want to know when three utility motors using 30V start and when they > end. When a motor starts it gets 30V. Actually they should get 24V but > occasional bursts to 30V are normal. The motors themself can handle the > extra voltage. > > What is the simplest way lower the voltage to 5V for my LPT port? I've > done simple electronics but a simple schematic would be great. I want to > know when each of the motors start. The safest way to couple signal from a "dirty" source -motors are notorious sources of noise and spikes- into a logic circuit is to use an optoisolator, a device with a lamp (usually an LED) on the dirty side and a phototransistor on the logic side. These are common parts, available from any of the online distributors. You connect the phototransistor side between a logic input and ground, with a pullup resistor. The LED side goes across the motor, with a series resistor whose value depends on the motor voltage and the current required by the LED. Another approach is a simple 6:1 resistive voltage divider, but you have to protect the logic input from overvoltage and from the negative voltage you get when you switch the motor off. Two diodes may be enough: one from the logic input to ground (anode to ground) to catch the negative back EMF from the motor, and one from the logic input to the 5V logic supply (anode to the logic input) to dump any overvoltage spikes into the 5V supply's filter capacitors. The optoisolator is safer. They typically offer several hundred volts of isolation. | ||||||||||||||||||||||||||||||||||
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Posted by Jamie on September 19, 2008, 6:52 pm
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spam_filter@invalid.nil wrote: > I'm using a computer to gather data using LPT1 port. The input pins of the lpt
When
> accept 0-5V. > > I want to know when three utility motors using 30V start and when they end. > a motor starts it gets 30V. Actually they should get 24V but occasional bursts
to
> 30V are normal. The motors themself can handle the extra voltage.
> > What is the simplest way lower the voltage to 5V for my LPT port? I've done > simple electronics but a simple schematic would be great. I want to know when > each of the motors start. Using a Photo coupler is the safest method that I know of. Just pull one of the input pins of your port using the photo output transistor. Since you stated 30 V's maybe the max at times I would use ~ 2 thirds of the LED (If) which is ~ 45 ma. R = (30-1.2)=(28.8)/0.045 = 640 ohms. W = 0.045*1.2 = 0.054 watts. http://www.qsl.net/n4xy/PDFs/Semiconductor_Data_Sheets/4n35_37.pdf P.S. Might be advisable to use a zener diode of around 30 volts so that it can be protected from reverse voltage exceeding (Vr) 6 and forward voltages exceeding 30 volts. If this is a brushed motor, it can generate inductive energy that isn't safe even for the coupler. A cheap zener diode helps this out in minor cases and the photo coupler helps in major cases to protect the computer. http://webpages.charter.net/jamie_5" | ||||||||||||||||||||||||||||||||||
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Posted by John Fields on September 19, 2008, 7:16 pm
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On Fri, 19 Sep 2008 18:52:46 -0400, Jamie >spam_filter@invalid.nil wrote:
> >> I'm using a computer to gather data using LPT1 port. The input pins of the lpt
When
>> accept 0-5V. >> >> I want to know when three utility motors using 30V start and when they end. >> a motor starts it gets 30V. Actually they should get 24V but occasional
bursts to
>> 30V are normal. The motors themself can handle the extra voltage.
>> >> What is the simplest way lower the voltage to 5V for my LPT port? I've done >> simple electronics but a simple schematic would be great. I want to know when >> each of the motors start. >
>Using a Photo coupler is the safest method that I know of. > Just pull one of the input pins of your port using the photo output >transistor. > > Since you stated 30 V's maybe the max at times I would use ~ 2 thirds >of the LED (If) which is ~ 45 ma. >R = (30-1.2)=(28.8)/0.045 = 640 ohms. >W = 0.045*1.2 = 0.054 watts. --- P = Iled (Vin - Vled) = 0.045A * (30V - 1.2V) ~ 1.3 watts --- >
>http://www.qsl.net/n4xy/PDFs/Semiconductor_Data_Sheets/4n35_37.pdf > >P.S. > Might be advisable to use a zener diode of around 30 volts so >that it can be protected from reverse voltage exceeding (Vr) >6 and forward voltages exceeding 30 volts. --- Missed this, did you:? View in Courier: 1/2 WATT 30V----+--[1000]--+------>4.7V
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[MOTOR] [1N5230B] | | GND>---+----------+------>GND
JF | ||||||||||||||||||||||||||||||||||
>accept 0-5V.
>
>I want to know when three utility motors using 30V start and when they end. When
>a motor starts it gets 30V. Actually they should get 24V but occasional bursts