Decided to take my mind off the INS for an evening and mess around with some engine instruments that I have out of an old Boeing 747 cockpit. The instrument in this posting is actually quite simple. It takes 115V 400Hz power to drive the instrument logic and a frequency input that simulates the tachometer attached to the compressor stage of the engine. That's it!
The tach input works well with a +5V pulse of about 40% duty cycle. The frequency ranges from 0 to about 75Hz. The instrument then does a frequency to DC conversion which positions the needle and the linked digit drum to the right tachometer value. The tach signals can be created with any Counter output available with most microprocessors.
Below is a short video showing the instrument in action. It's a bit of a noisy instrument mainly because of the 400 cycle hum:
The tach input works well with a +5V pulse of about 40% duty cycle. The frequency ranges from 0 to about 75Hz. The instrument then does a frequency to DC conversion which positions the needle and the linked digit drum to the right tachometer value. The tach signals can be created with any Counter output available with most microprocessors.
Below is a short video showing the instrument in action. It's a bit of a noisy instrument mainly because of the 400 cycle hum:
This is great Curd. Where do you get the 115V 400Hz power from?
ReplyDeleteSoeren, thank you for your comment on the blog. 400Hz power is the most common power form on aircraft, and perhaps one of the hardest things to find when you are not on an aircraft. There are several way for you to get access to 115V 400Hz power: a) you can use a motor generator powered from DC (you can find those on e-bay from time to time) but they require a rather large DC source (typically 24V with 40 or 50A or more), b) you can get a static inverter that is also powered from a DC source (they are typically smaller and don't need quite as much DC power ... search for static inverter on ebay) and lastly c) you can get a standalone inverter that runs from your 120V/50Hz or 220/60Hz wall outlet. I invested in a larger 5K 400Hz Inverter a few years ago that I am using for the L-1011 project and then I also have a smaller inverter that I use on my workbench. Hope this helps. By the way: Please be careful when handling any high power/high current devices such a 400Hz Inverter because they can lead to personal injury when handled incorrectly. Always use a fuse between the inverter and the instrument ... in the blog posting above I used a 0.5A fuse.
Delete