PhotoNinja
New Member
Okay, here's the rundown:
I'm a undergrad mechanical engineering student and am taking a basic circuits course for non-electrical majors. We've been assigned a cumulative final project and I have chosen to build a simple digital tachometer.
The idea is to light an array of LEDs based on relative motor speed (something like you would see on the steering wheel of a high performance car). The faster the motor is running, the greater number of lit LEDs.
I'm not so interested in finding the actual RPM of the motor, simply the speed relative to the max or min. For example, if the motor is running at 75% of the max speed, 75% of the LEDs will be lit.
My group has access to a 3V Olimex microcontroller/development board.
Here's where I need some help: I'm a bit unsure as to what sort of sensor I will need to read off RPMs (likely not greater than 1500). I'd like to do this as cheap as possible since, after all, it's only for a simple project.
I was perhaps thinking about some sort of light sensor (like the ones in the Lego Mindstorms kits) with a white/black cylinder or disc. The sensor would read a stripe of the opposite color. I would consider hacking a LEGO sensor, but I'm not sure if it is capable of reading fairly fast transitions between colors (something around 350 RPM). Perhaps someone can shed some light (Ha, no pun intended)?
People have also suggested potentiometers and encoders. So far, encoders have been fairly expensive (and I have no idea how to tell if they're compatible with the microcontroller). As for potentiometers, I've only seen them used in volume knob-like applications. Would a pot be viable in a high(er)-speed (again, somewhere around 350 RPM) application?
This will all be mounted to a small (likely DC) motor which will be turning a flywheel and a simple 3-speed LEGO transmission.
So, I suppose the shortlist is this:
- Cheap
- Compatible with the microcontroller
- At least a 20 RPM resolution (I'd like perhaps 10 LEDs covering the range of 350 RPM)
- Can be mounted on something small (think Lego motor)
I think that's about it for now. Any info would be awesome, thanks in advance!
I'm a undergrad mechanical engineering student and am taking a basic circuits course for non-electrical majors. We've been assigned a cumulative final project and I have chosen to build a simple digital tachometer.
The idea is to light an array of LEDs based on relative motor speed (something like you would see on the steering wheel of a high performance car). The faster the motor is running, the greater number of lit LEDs.
I'm not so interested in finding the actual RPM of the motor, simply the speed relative to the max or min. For example, if the motor is running at 75% of the max speed, 75% of the LEDs will be lit.
My group has access to a 3V Olimex microcontroller/development board.
Here's where I need some help: I'm a bit unsure as to what sort of sensor I will need to read off RPMs (likely not greater than 1500). I'd like to do this as cheap as possible since, after all, it's only for a simple project.
I was perhaps thinking about some sort of light sensor (like the ones in the Lego Mindstorms kits) with a white/black cylinder or disc. The sensor would read a stripe of the opposite color. I would consider hacking a LEGO sensor, but I'm not sure if it is capable of reading fairly fast transitions between colors (something around 350 RPM). Perhaps someone can shed some light (Ha, no pun intended)?
People have also suggested potentiometers and encoders. So far, encoders have been fairly expensive (and I have no idea how to tell if they're compatible with the microcontroller). As for potentiometers, I've only seen them used in volume knob-like applications. Would a pot be viable in a high(er)-speed (again, somewhere around 350 RPM) application?
This will all be mounted to a small (likely DC) motor which will be turning a flywheel and a simple 3-speed LEGO transmission.
So, I suppose the shortlist is this:
- Cheap
- Compatible with the microcontroller
- At least a 20 RPM resolution (I'd like perhaps 10 LEDs covering the range of 350 RPM)
- Can be mounted on something small (think Lego motor)
I think that's about it for now. Any info would be awesome, thanks in advance!
Last edited: