Adding an RPM Readout for a Home Made CNC Mill


[Rui] recently put the finishing touches on his homemade CNC mill, which utilizes a dremel-like rotary tool. The problem with using rotary tools for this kind of application is you don’t really have an accurate speed readout… so he designed his own RPM gauge.

The sensor is in itself very simple. He’s using a TLE4935L hall effect sensor, a spare 16FE88 microcontroller, a Nokia LCD, and one tiny neodymium magnet. The magnet has been carefully epoxied onto the motor fan, with the hall effect sensor close by. He’s also built a guard around it, just in case the magnet decides to fly off at high speeds.

During testing he hooked up the hall effect sensor to both his home-made circuit, and an oscilloscope to confirm his findings. Once he was assured everything was working properly he sealed it off and mounted the LCD above the spindle as a nice digital readout.

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Arduino Tachometer tutorial

This tutorial will guide you through the process of building a tachometer around an Arduino. Tachometers are used to measure rotation rate in Revolutions Per Minute (RPM). You don’t need much in the way of hardware, this version uses an Infrared beam to measure fan speed. As with last year’s PIC-based tutorial, [Chris] is using a character LCD to output the reading. Wiring and driving the LCD ends up being the hardest part.

An IR transmitter/receiver pair are positioned on either side of the fan. When the blade passes in between then, the receiver shuts off a transistor connected to one of the Arduino’s external interrupt pins. He shows how to use this interrupt to measure the amount of time between the passing of each fan blade. If you divide for the number of blades, and average the reading for greater accuracy, you can easily calculate RPM.

Another alternative would have been to use a reflectance sensor which allows to for the transmitter and receiver to both be on the same side of the fan.

Simple sensors to calculate RPM

Ever wonder how to calculate revolutions per minute using a microcontroller? This project shows you how by purposing an IR emitter and detector and a computer fan. As the fan blades spin they disrupt the beam of infrared light between the emitter and the receiver. This results in a waveform on the receiver’s circuit which can be easily used to trigger interrupts in any microcontroller. In this case a PIC 18F452 monitors the detector’s signals for a rising edge. By measuring time data between interrupts the period can be established and RPM calculated. You can see a video of the test rig after the break.

So what can you use this for? It’s the method that most spinning POV displays use to stabilize the display. You won’t be limited to an IR sensor, but can use a hall effect sensor in the same basic fashion.

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Vehicle information display hacks

We’ve had a few folks send us info about their vehicle display hacks after seeing [Will O'Brien's] motorcycle computer a few days ago.

On the left we have a display for an electric vehicle. [S1axter] is using a 4.3″ TFT screen to display charge information for each battery cell in the car. An ATmega88 collects the data and sends it to a breakout board with an LCD controller on it.

To the right is a display from a Formula Student project. a Matrix Orbital GLK19264-7T-1U LCD display provides a lot of real estate for displaying data. Right now [Alan] is still in the early prototyping stages, but the video after the break demonstrates the RPM readout using a function generator. It’s not shown in the video, but he tells us that he’s since tried it out with the engine and has a PIC 16f877 reading temperate data from the electronic control transmission sensors in addition to the RPM data.

Correction: Thanks to [j] for correcting our mistake. This is a Formula Student car.

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Custom motorcycle display


[fibra] has been slowly building a custom controller for his motorcycle. It’s an automated chain oiling system that varies application based on RPM. The LCD can show wheel RPM, voltage, time, date, air, and engine temperature. A separate driver board has a MOSFET for controlling the oiling valve. The real gold here is the attention to detail. He built a one off circuit board. The case is laser cut acrylic that he then shaped. The box is molded smoothly into the original instrument cluster using epoxy. It’s excellent work that could be mistaken for a commercial product.

3-digit frequency meter

Flow sensors are useful tools for collecting data on the rate of liquid usage, but they need a device to display the data they collect. This three digit frequency meter was designed by [Turbokeu] to do just that, converting a Swissflow SF800 flow sensor’s square wave signal (similar to fan RPM signals) into an numerical expression of liters per minute on a 3 digit LCD. Fan RPM is

[Turbokeu] provides detailed schematics of different configurations for the frequency meter as well as schematics of the layouts of the two PCBs that are used. Even if you don’t have an immediate use for a frequency meter, his clean and readable schematics are worth a look in their own right. The display is installed on front of a tower case along side a CPU speed display.

[via YourITronics]