Ding. You have got a USB desk Bell. Version 2!

Based on an original instructable made a few years ago I tried to make a USB Bell.

I ran into some problems with winding the electromagnetic coil. There is just no way that a hand wound coil running off USB is powerful enough to pull down the clapper. I have my doubts to the original tutorial but it gave me inspiration.

I replaced the hand wound coil with a 5v solenoid that is available on eBay, Amazon or any other hobby electronics site.
I kept the original schematics the same but replaced the over the top ARM MCU with a simple USB to Serial peripheral. I hacked the rs232 end off and used pin 7 (RTS) (pictured as 1 in the schematic) to trigger the NPN transistor instead.



This works really well- especially that the usb to serial is plug and play. So just plug it into any Windows machine and a new com port will show up. You can use any programming language to open the port and set the RTS enabled to trigger the solenoid and RTS disabled to cut it out.



I leach 5 volts from the USB side. One thing to note is that there is a limit of inrush current in USB specifications of 470uf. It would be best to use a capacitor of 470uf for the coil to avoid USB reset. I use a 220uf capacitor, which works well. When the driver initialises you get 3 series of 2 dings, not sure why but at least you know it works.

Here is a video response I made to the original schematics designer. But he has not replied to any of my messages on any site...

Instead of being triggered by emails I wrote a Windows service we use at work to monitor new orders and new sites on a specific project. A colleague made a snazzy dashboard so we can see what's happening on our soon to be 2000+ websites. It will be interesting to see how the bell copes with hundreds of orders a day. It might drive us crazy though ... :)





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