stop time with an led stroboscope!

by:IPON LED     2020-05-15
Stroboscope works by producing a very short but very bright pulse of light.
If the frequency of the light pulse is correct, the rotating object will be illuminated in the same position during each flash, thus presenting a still appearance.
This phenomenon is called strophobic effect.
The Stroboscope effect is actually a sample phenomenon, which is the result of under-sampling.
If you are familiar with digital signal processing, you may realize that the sampled signal generates an \"alias\" depending on the sampling rate used \".
A signal sampled at less than twice the frequency can produce a result called an alias with a lower frequency than the original signal.
If the signal is sampled at exactly the same frequency as the input signal, the sampling is performed at the same time in its cycle, and therefore, the same value is always read.
Because the result of each sampling is the same value, the resulting sampling signal indicates that it is displayed as a DC value, not an alternating waveform of the actual signal.
Therefore, the original signal is reduced to the DC signal in frequency.
Stroboscope has the same concept.
In the eyes of the observer, the actual rotation speed will drop to zero, resulting in false perception that the object is stationary.
When the strophobic frequency is an integral part of the rotational frequency, the object also appears in a static state, such as a half, 1 out of 3 or a fourth grade.
This is because these conditions also cause the object to be illuminated each time it is in the same position.
If the strobe frequency is slightly lower or higher than the rotation rate (
Or an integer fraction of the rotation rate)
Object, it will appear to rotate slowly forward or backward.
In these cases, the rotation speed in the observer\'s eye has dropped to a speed slightly above zero.
If the rotating object has multiple identical sectors, such as the spokes of the wheel or the blades of the fan or propeller, the appearance of the rotating object illuminated by the flash can show more complex behavior.
In these cases, when the period of the strophobic frequency is an integer multiple of the rotation period divided by the number of sectors, the object may appear static.
If a single sector is similar enough in appearance that they are the same as the observer, then the object will appear static at any frequency of strobography where any of the same sectors are in a given position.
When the strophobic frequency is swept out, the observer may notice several points where the rotation seems to slow down first, then stop, and then start to rotate in the opposite direction.
The light pulses produced need to be very short and very bright.
They need to be short, because the longer the light opens, the more positions the object will change during this time.
If the object moves significantly during lighting, the audience will feel that it is ambiguous.
This is similar to the shutter speed of the camera.
Since the pulse needs to be very short, it also needs to be very bright in order to provide enough lighting for a short period of time.
A stroboscope usually uses a xenon flash to produce a brief burst of light.
The project uses white LEDs instead of xenon flash lights.
The strength of the xenon flash is much larger than that of the LED array.
The pulses produced are not as bright as those produced by xenon tubes.
Because this LED-based flash hardly provides a xenon version of the lighting level, it helps if used in lower light conditions.
The driver circuit described later is designed for use with the LED array.
A suitable LED array can be created by modifying a ready-made LED flashlight or lantern.
I have made some changes to these ready-made products to make them more suitable for use with drivers, which I discussed in detail in the following steps.
In normal use, the LEDs in the flashlight are continuously powered by the DC current of the battery.
This type of flashlight usually consists of only LEDs, one or more current limiting resistors, and one switch.
When continuously driving in a flashlight is used, the current in each LED is usually limited to about 10 to 30 mA levels.
LEDs need to be as bright as possible in order to be used in the flash, but they must also be driven by very short pulses to prevent objects from looking too blurry.
In other words, the duty cycle of the LED driver will be very low.
If driven with a higher current, the led can produce a brighter output.
In order to get the maximum illumination from LEDs under such a low duty cycle drive, they should be driven at the highest possible current without the risk of damage.
The most commonly used led Size in flashlight is T-1 ¾ size.
You will most likely not be able to find the part number or data sheet of the actual LEDs used in the off-the-shelf flashlight, but you can understand the reasonable maximum current they can drive by checking the specifications of other low-cost LEDs in the same package.
I checked the datasheet of several low cost White led for T-led
Size 1, typical rating of 100 mA for maximum pulse current found.
To get the maximum illumination from the light, it should be configured so that each LED carries current close to the maximum pulse current rating.
When I modify the lights described in the following steps, I choose to drive them at about 75% of the maximum pulse rating, about 75 mA each.
I chose not to drive under the assumed 100 mA pulse current to provide a certain margin to help ensure they are not damaged.
The driver described here is designed for a 12 volt operation.
The flashlight I modified was designed to be powered by a lower voltage, usually in series with 3 or 4 AA or AAA batteries.
The increased drive current and different supply voltages make it necessary to modify these ready-made lamps before they can be used with the drive circuit.
Before the modification: the first LED flashlight I modified was a small unit that sold for about $4 at the port freight.
It contains 24 LEDs in the main light and 3 LEDs in the smaller light.
The button switch cycles through different modes: main light, turn off light, small light, turn off light, etc.
The schematic diagram below shows how this product is designed.
When I opened the case, I was surprised at how the led was connected.
Note from the schematic that all 24 LEDs are in parallel.
I always build the LED circuit with each string of LED having its own resistor.
The theory behind this approach is that if they are directly parallel, there will not necessarily be equal sharing of current between them.
The results may include some led dimming due to a decrease in current, while others may be damaged due to excessive current.
Placing a separate resistor in each string ensures that the current of the branch through series is basically balanced.
Prior to modification, the main array of 24 LEDs had a 1 ohm current limiting resistor in series with it.
The lamp is powered by 3 AAA batteries (4. 5 Volts).
The positive drop of LEDs is about 3. 5 volts.
I observed that the battery voltage would drop from 4.
Even with the new battery, 5 v drops to about 4 V when the light is on.
Therefore, in the normal operation of the unmodified lamp, the total current through the bank group is about: ledledled_bank = (4. 0V-3. 5V)/ 1 ohm = 0. 5 Amp.
If the current is evenly distributed between LEDs, the current through each LEDs is: led each _ led = 0. 5Amp/24 = 21 mA.
Modification: using the 12 V power supply used with the drive circuit, I can utilize the power more efficiently by changing the LED connection.
I modified the PCB connection to split 24 Parallel LEDs into two groups with 12 Parallel LEDs in each group.
As shown in the figure, this requires cutting marks on the PCB.
Two sets of 12 LEDs are then placed in series.
Please refer to the schematic diagram below for the modified lights.
I also chose to add a reverse protection diode to the LED array to prevent it from being damaged when the wiring is wrong.
I assume the voltage is reduced to 0.
The voltage of this diode is 7 v.
Recall that there is also a series diode between the input of the battery/power supply on the driver PCB, which must also be taken into account.
As mentioned earlier, I chose to make the pulse current about 75% of the assumed 100 mA maximum pulse current to allow a certain margin.
Note that the total current through the array is 12 times that of a single LED current.
The new current limiting resistance value is calculated as follows: R = (12V – 3. 5V -3. 5V– 0. 7V -0. 7V)/ (12 * 75mA)R = 4 ohms.
Even when the led is driven horizontally at current levels close to the 100 mA pulse current rating, the brightness of the light is not as large as the brightness generated by the original light.
Such a low duty cycle is inevitable.
Operating at a higher current may destroy the LEDs, and operating at a higher duty cycle can make the moving object look blurry.
If larger lighting is needed, a custom LED array with more LEDs needs to be built.
Before modification: The second flashlight I modified is the 65 LED model.
There are two settings for the flashlight, one is to turn on 21 of the 65 LEDs and the other is to turn on all 65 LEDs.
The button switches the loop between modes.
The schematic diagram shows how this flashlight is constructed.
As I found with 24 LED lights, the LEDs connect directly in parallel when I turn it on and check the connection.
Although it is generally believed that the led should not be connected directly in parallel, it obviously works fine here as well.
When viewing, the brightness of the led in the device looks uniform, so the current through them must be shared relatively evenly.
So maybe you can place LEDs in parallel like this.
However, even with this in mind, when I build any LED array, I will continue to use the recommended practice of using individual resistors in each string.
Therefore, the total current through the bank is about: ledled_bank = (6. 0V-3. 5V)/ 1 ohm = 0. 5 Amp.
If the current is distributed fairly evenly between LEDs, then the current through each LEDs is approximately: led each _ led = 0. 5Amp/24 = 21 mA.
Modification: The array will be driven by 12 V.
With the 12 V power supply, I can make more efficient use of the power by changing the LED connection.
I modified the PCB connection to divide 65 Parallel LEDs into two groups, one with 33 Parallel LEDs and the other with 32 Parallel LEDs.
As shown in the figure, this requires cutting marks on the PCB.
Two sets of led are then placed in series.
Please refer to the schematic diagram below for the modified lights.
I also chose to add a reverse protection diode to the LED array to prevent it from being damaged when the wiring is wrong.
I assume the voltage is reduced to 0.
The voltage of this diode is 7 v.
Recall that there is also a series diode between the input of the battery/power supply on the driver PCB, which must also be taken into account.
As mentioned earlier, I chose to make the pulse current about 75% of the assumed 100 mA maximum pulse current to allow a certain margin.
Note that the total current through the array is 12 times that of a single LED current.
The new current limiting resistance value is calculated as follows: R = (12V – 3. 5V -3. 5V– 0. 7V -0. 7V)/ (33 * 75mA)R = 1.
5 ohm even when the led is driven horizontally at a current level close to the 100 mA pulse current rating, the brightness of the light is not as large as the brightness generated by the original light.
Such a low duty cycle is inevitable.
Operating at a higher current may destroy the LEDs, and operating at a higher duty cycle can make the moving object look blurry.
If you need a larger amount of lighting, you need to build a custom LED array with more LEDs.
If modifying a ready-made lamp does not meet your needs, you can build a custom LED array using a single LED.
How to connect LEDs to arrays has been reported many times on this site and elsewhere.
I have sorted out my own brief description of the process of designing LED arrays, which is covered in this section.
Simple LED array design: If you want to drive a string of LED with the specified current (I_LED)
From a known voltage source (Vs)
, You can use the following procedure to determine how many LEDs can be placed in series and what series resistor values are required to set the required current.
The basic steps in the design process are as follows.
Reference schematic diagram. 1)
Sub-supply voltage (Vs)
Through forward voltage (Vf)
LED you are using.
The forward voltage is the voltage drop when the LED is biased forward.
The diagram of forward current and forward voltage will have a very steep knee, because to get most of the change in forward voltage, a significant change in current is required.
The forward voltage depends on the temperature, and the forward voltage is higher at a lower temperature (
Negative temperature coefficient).
The supply voltage must be at least as large as the forward voltage of a single LED to light the LED.
Therefore, in order to be able to light up an LED, the result of this calculation must be greater than 1. 2)
Rounding the results from step 1 to the nearest integer.
The result gives you the number of LEDs that can be connected in series at a given supply voltage and LED forward voltage. 3)
Multiply the result of step 2 by the LED forward voltage.
This gives the sum of all the forward voltage drops of the led in the series string. 4)
Subtract the result of step 3 from the supply voltage.
The result is the amount of voltage that will drop on the current limiting resistor. 5)
Divide the result in step 4 by the current to flow in the LED string.
The result is the resistance value of the current limiting series resistance.
Select a resistor of the right size to ensure that it is not damaged due to power consumption.
The power in the current limiting resistor is: pwr _ r _ current _ limit = (I_LED^2)
* R _ current _ limit selects a resistor with a rated power greater than the pwr _ r _ current _ limit value.
This is the lowest rated power if the array is driven with a 100% duty cycle.
If the array will be used in applications that are pulse at a rather high frequency rather than continuously open, the rated power determined above can then be multiplied by the maximum duty cycle to obtain the average power.
The stoner application has a fairly low duty cycle, with a maximum duty cycle of about 3% for the design described in this manual.
If you connect the number of led determined in step 2 to the resistance determined in step 5 and apply Vs in the string as shown, then the led will carry the required current (I_LED)
When the string is applied to the supply voltage, the required current will flow through the LED string.
Each LED in the string will carry the same current, so each LED should have comparable brightness.
If a larger LED array is required, several identical strings can be placed in parallel as needed, each with its own current limiting resistor.
The total current to be extracted from the power supply will be equal to the number of strings multiplied by the current in a single string.
If the power supply Vs is connected directly to the battery, then of course the Vs drops when the battery is discharged.
The LED current will decrease and the brightness of the LED will also decrease.
If this is not acceptable then Vs should be a regulated voltage source.
For this I chose not to use a typical project chassis.
Instead, I made a sandwich.
The whole component looks a bit ugly, but it works.
See pictures for more information.
I used the 1/8 thick plastic plate and separated it with light aluminum channel material.
The knobs and switches are located on the rear panel.
Most circuits are built on a small custom PCB connected to the interior of the rear panel.
The AA battery stand is mounted on the next panel of the \"sandwich.
I have 24 LED lights installed on my front panel.
A short harness connects 24 LED lights to the drive circuit output jack.
If larger lighting is needed, the user can disconnect 24 LED lights and connect a larger LED array at any time.
The software provides two modes, strobography mode and trigger strobography mode.
In all modes, the conduction time of the pulse is adjustable from 50 to 562 microseconds using a potentiometer.
The user needs to adjust the opening time of the pulse as needed to get a clear image.
The longer the time, the greater the lighting will be generated, but depending on the speed at which the object moves, it may appear blurry.
In general, as the speed increases, the object will appear more blurry because it will move more objects during the light pulse.
Strophobic frequency in strophobic mode (
Total period, as shown in the timing diagram)
Determined by the frequency setting potentiometer.
The frequency range of stroboffs is separated in normal mode stroboffs.
One mode covers the range from 5Hz to 15Hz, the second from 15Hz to 30Hz, and the third from 30Hz to 50Hz.
When there is a to Button in the stroboscope mode ,(
Jogging forward and jogging backward)
The frequency of the pulse is allowed to be slightly increased or decreased from the nominal value of the frequency selection input setting.
By changing the frequency a little in this way, you can rotate the position of the object forward or backward.
Once the object is in the desired position, the switch is released and the pulse frequency is returned to its normal value.
In the trigger flash mode, the light flashes after the trigger signal is detected (
Low signal).
The timing diagram shows the relationship between the trigger pulse and the output pulse.
This mode is useful if the sensor is installed on the machine in order to generate a low trigger pulse for each rotation or cycle.
The circuit detects this trigger and then generates a pulse after the delay determined by the delay input.
In this way, the flash will automatically synchronize with the speed of the object.
In Trigger strophobic mode, the function of setting on time is the same as in strophobic mode.
The second potentiometer (
For frequency selection in other modes)
Instead, it is used to set the delay between trigger detection and flash output.
The delay can be set between about 50 ms and 51 MS, in increments of 200 ms, and the reverse jogging input is used as the trigger input.
Output this input to an external connector in order to connect it to the sensor.
Any type of sensor can be used, such as infrared photo sensor, Hall effect sensor, etc.
Once the driver board uses a microprocessor to read the user input potentiometer and switch and stroke the LED array accordingly, the sensor must produce a low pulse.
The microprocessor has six I/O pins.
The time and frequency can be flexibly controlled independently using a micro-controller.
The software allows to set the strobography frequency between 5Hz and 50Hz (
Within three frequency ranges)
, It allows the on-time of the pulse to be set between 50 microseconds and 562 microseconds.
The power input can be entered via an external Jack, J1, or battery pack.
Diodes D2 and D1 are used to isolate the battery and external power supply, and if they are connected at the same time, they can also prevent circuit damage if the power input polarity is opposite.
5 v regulator LM7805 regulator U2 provides 5 v regulated voltage for the pulse generator circuit.
There are electrolytic and ceramic capacitors (
C1, C2, C3, C4, C9)
Filter the input and output of the regulator.
The microprocessor uses its internal A/D converter to read two analog inputs (AN2and AN3).
These analog inputs read the settings of the potentiometer R1 and R3, which set the opening time of the flash and the frequency of the flash.
R2, c2, R4, and C7 are used as high pass filters on these analog inputs.
Time and frequency are independently controlled by each other.
The software generates output pulses based on time and frequency readings.
Mode Select enter the third analog input (AN1)
Select Input for read mode.
Mode Select Input reads the voltage on the common terminal of the multi-position rotary switch.
The common terminal of the switch is connected to 5 volts through the resistor R9 and connected to the ground through one of several different resistors (
R11, R12, R13, or R14)
, Depending on the position of the rotary switch.
Each switch position will cause the voltage setting at the mode selection analog input to be different.
The microprocessor A/D converter reads the analog value and selects the appropriate working mode based on that value.
The microprocessor also reads two digital inputs (GP5 and GP3)
Connected to the normally open SPST switch, its function depends on the mode of operation selected.
These switch inputs are pulled to 5 v by R5 and r7.
R6 and R8 are used to prevent the input of U1 from being damaged when the input is short-circuited to the power supply.
In strophop mode, these switches are used to move strophop frequencies up and down slightly in order to \"relocate\" the object to a more appropriate position as needed.
In Trigger Flash mode, the jog reverse input is also used as a trigger input.
This connection is through a 9-pin D-sub connector (J3)
Interface for use with external sensors.
Any sensor or other external circuit, such as a light circuit breaker or Hall switch that can pull this line low to ground, can be used to trigger the flash.
Current limit output is also provided on D-
Sub-connectors, power the infrared LED if the light interrupt switch is used.
This line is connected to 5 v through a 200 ohm resistor.
See theschematic see signal provide D-
Sub and how to connect them to the interface of the light interrupt switch.
An example of an infrared optical sensor is shown at the bottom of the schematic diagram.
The pulse output of the LED driver output microprocessor is applied to the bottom of the FET Q1, allowing the current to flow through the LED array.
The R16 is used to keep the FET gate low so that it does not float high.
The R15 is connected in series with the gate of the FET to prevent gate ringing due to the parasitic capacitance of the FET.
The LED array is connected to the output connector J2 of the drive output.
The LED array forward connection is directly connected to the 12 V power supply and the current path through the array is completed through the FET.
The software is written in PIC assembly language.
Source code (*. asm file)
Assembly files for programming (*. hex file)
Included here.
I also included a PDF of the flow chart showing the functionality of the software.
Update: I added a second hex file for use as per the user\'s request. (12F683_STROBE_-NEW. HEX)
The difference between this file and the original file is that it has a longer trigger delay capability in trigger strobography mode.
It will allow 360 degrees or rotations at speeds as low as 250 RPM.
The video in the first part contains an example of the stroboscope being used.
Here\'s a brief discussion of what\'s happening in each example.
Example 1: one way for fan blades to observe strophobic effects is to look at the fan.
Adjust the frequency of the flash and observe as the direction and speed of the fan blades change.
The following picture shows the fan rotating at a speed of about 600 rpm or 10 rpm.
It was filmed when the strobography frequency closely matched the fan speed.
This photo was taken with the shutter open for 1 second.
If the flash is not synchronized with the fan, the picture will be completely blurred.
When manually matching the strobography frequency to the speed of the object, it is difficult to make the motion completely stop, because even if the speed difference between the object and the Flash is very small, it will cause some visible rotation.
To highlight some of the stroboscopic effects, I put a label with numbers on each of the five blades of the fan.
When the flash flashes at a speed equal to the rotational speed or its integral part, the number appears to remain stationary with the fan blade.
At the frequency of each time the strobography is turned on, the different blades are in the same position as the previous one, and the blades seem to be stationary, but the numbers count up or down.
Example 2: The interesting effect can be seen in the video of the drill bit drilling on the plate.
In the case of strophobic frequency sync, the bit looks static even if it rotates at about 660 rpm.
When the drill bit is inserted into the plate, the load on the drill motor increases, so the rotation speed drops slightly.
As the speed decreases, the strobography frequency is not quite in sync with the frequency of the bit, so it looks like it\'s spinning, but it\'s slow.
As the drill bit moves down, you can see that the holes in the plate are forming and the pieces fly to one side and even think that the drill bit seems to be almost stationary.
Example 3: This demonstration of lathe uses trigger switching mode.
I installed a reflective infrared sensor on the bracket on the head of the lathe.
This is a sensor that encapsulates both the ir led and the IR photoelectric transistor in one package, as shown in the following figure.
The transistors and LEDs in the package are installed together so that they all point down at a certain angle.
When the IR reflection object passes below the sensor at the correct height, the IR light is reflected back onto the photoelectric transistor, which then turns on and pulls the trigger input low.
There is a black tape package on the card plate of the lathe, and a small piece of white tape.
When the part of the white tape passes under the sensor, the infrared light emitted by the LED in the sensor is reflected back to the photoelectric transistor in the sensor, and the trigger input is pulled low, triggering the flash.
It needs to be wrapped in black tape, because the IR light reflected by the shiny metal of the lathe chuck is enough to trigger the sensor incorrectly.
The video shows that even if the speed increases, the Chuck appears to be stationary because the flicker is controlled by the trigger signal of the sensor.
As the delay between the trigger signal and the Flash increases and decreases, the position of the Chuck can be seen moving back and forth.
Conclusion: these are just a few simple examples of strophobic effects.
There are a number of other interesting presentations to do, including watching the speaker cones and falling drops.
I hope you have found useful information here and have been successful in building your own flash.
If you do, please share any cool apps or demos you find for your stenclight!
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