How fast can a Fidget Spinner spin? Well, it depends on what spins it. Let's use compressed air.
That sounds fast, it's actually scary to hold!!! But how fast?
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To make the measurement we used a simple LED as a sensor. A bright light shines down onto the LED. The arms of the Fidget Spinner block the light as they move over the LED creating electrical pulses.
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The sensor LED is connected to a Tektronix MDO4104C to measure the pulses. The scope (along with a few thousand other features) allows an engineer to quickly study waveform measurements with cursors. After a little math we get our answer; well over 10,000 RPM.
From time to time the level shift module pictured above has come in handy. They do a great job shifting 3.3VDC to 5VDC logic or 5VDC logic to 3.3VDC logic. The cost is about $1USD and hookup is simple. Of course they are designed for low speed digital signals but, we wondered how the module would handle higher speeds.
Performance was very good, especially considering these module are often used in the 100KHz and below range. Leveling from 5V to 3.3V had better results. The signals start looking ridiculous over 1MHz. Take a look at the scope shots below.
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3.3V Level Shifted to 5V at 10KHz, 100KHz, 500KHz, and 1MHz
(Yellow = Input; Blue = Output)
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5V Level Shifted to 3.3V at 10KHz, 100KHz, 500KHz, and 1MHz
For about a $1.50 USD eBay sellers will ship out to you the servo tester pictured above. It's an amazing value to let you verify that the cheap servo you also got from eBay even works. It's also great to help understand the MIN, CENTER, and MAX positions for any servo based RC or uC project.
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Basically, servos motors are controlled by receiving pulse train signals. The eBay servo tester is capable of producing this required pulse train. Jameco has an easy to follow tutorial. The image below shows that a 1mSec pulse width sends the servo full left. 1.5mSec centers the it. 2mSecs move the servo full right. Jameco explains it all very well.
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The servo tester has three setting:
MANUAL: allows the servo position to be
adjusted with a knob.
CENTER: sets the servo to it's center
position
SWEEP: continually sweeps the servo from it's MAX to MIN position (forever)
Connection is simple. One side of the servo tester is for power. The other side is where the servo under test conveniently plugs in.
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So.... let's use a Tektronix MSO5104B oscilloscope to look at the output of the servo tester and see what the heck is going on. In the screen shot below the servo tester control knob is set to full left (minimum). Sure enough, the pulse width as measured by the scope is 915uSec. That's pretty darn close to the 1mSec width in the drawing above.
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With the knob set to full right (maximum) the scope cursors show a pulse width
of 2.14mSec; pretty close to the ideal 2mSec in the drawing.
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Using the MSO5104B oscilloscope to zoom out on the signal we can see that the pulses repeat steadily every 20mSec. If you check the tutorial at Jameco you will know that is exactly what is expected.
----- Conclusion: Splurge the $1.50 USD and treat yourself to this handy device. It really helps to verify that a servo is actually working and in setting the movement limits on your project. Below are two short videos of the servo tester in action.
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Here a short video where I use a Tektronix AFG3252C to send the control pulses to the servo. The AFG3252C has infinitely more flexibility, but cost a few dollars more than the eBay option.
The Charger Doctor is a sub $2 device that displays voltage and current levels while charging a USB device. There have been several teardown write ups on the Charger Doctor. It's useful, but does have some limitations. For example, it doesn't charge iOS devices and it seems to effect the reliability of the WiFi connection on our Raspberry PIs. This made us want to take a closer look at what the output was doing.
Here we use a Keithley DMM7510 to monitor the Charger Doctor output. The DMM7510 is a precision instrument with 7.5 digits of resolution and 14 PPM accuracy. It has a touch screen interface with graphical output, advanced triggering options, cursors, and a whole lot more. Plus, it is fast (very very fast); capable of sampling at 1M/s. To sum it up, it's pretty darn cool!
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In the video the DMM7510 shows a decrease in voltage when the Charger Doctor displays current. Also, some instability when displaying voltage. But remember, the Keithley DMM7510 is a very sensitive instrument. The change in voltage looks big on the screen, but it is really very small.
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The overall voltage swing is only 7.536mV or 0.00753 Volts. That's not a lot.
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And taking a closer look at that instability when the Charger Doctor displays voltage we see that it is only 1.256mv peak to peak; that's just 0.001256 Volts. Really, that seems exceptional for a sub $2USD device.
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There is a lot of discussion on the web as to why iOS devices don't charge via the Charger Doctor. With the stability shown, I'm not sure why the Charger Doctor effects the WiFi reliability of the Raspberry PI, but I can say it does. We set the Keithley DMM7510 to camp on the Charger Doctor output signal and trigger on a larger glitch or voltage spike to give us a clue. After about 15 minutes the Charger Doctor remained stable within the trigger limits and we moved on with our life. We do have to take into account that the Charger Doctor was effectively unloaded while making these measurements and that could make a big difference.
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Thanks for stopping by.
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It takes some time for an electrical signal to travel down a wire or through a logic gate. Not much time, but some. It's called propagation delay (tpd) or "prop" delay. We had a 74HC04N on the breadboard from our recent Rasperry PI CPU Usage Tachometer project and decided (for reasons unknown) to measure the prop delay of this chip. The 74HC04N is a simple IC that turns a logic "0" into a "1" and turns "1" into a "0". It has "six" gates to "invert" digital signals; thus the name "hex inverter".
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For our measurement setup we used the Tektronix MDO4104B-6 oscilloscope. It has plenty of what it takes to make this simple prop delay measurement and we had one handy. Since passing through one gate inverts a digital signal, passing the signal through two gates (or any even number of gates) will invert that signal back to it's original logic level.
Here is a 5VDC signal propagating though two gates. The yellow trace is the input and the blue trace is the output after passing through two gates. Using the scope cursors we measure the prop delay at 12nS (nS or nanosecond = 10EE-9 seconds). That's an average of 6ns per gate.
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Here is a 5VDC signal propagating though all six gates. Again, the yellow trace is the input. The blue trace is the output. The scope cursors measure the total prop delay at 33.2nS (as well as some signal degradation from loading) for an average of 5.53nS per gate.
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Is that prop delay good or bad? Well, we have to consult the device datasheet. For a 5VDC setup NXP specs their 74HC04N at 7ns per gate typical, so our chip is beating the spec! As far as it being good or bad depends on your application. For most low speed hobby projects prop delay isn't even a consideration. If you are designing high speed circuits then race conditions and prop delay specs become important to your design.
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UPDATE: Special thanks to all the .EDU sites for checking in!
