THE cheapest homemade Casio to PC cable ever.

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All these cables do is convert voltage levels between​ 0V/3.3v TTL and the +/-v of RS232 which can be anything between 5v and 15v. Often -13v/+13v.. As serial ports are almost extinct it seems very roundabout to then convert RS232 to 0v/5v USB. Just convert directly between 3.3v TTL and 5v USB. Cut out the middle man. The cable designs shown in another post are historically interesting but becoming obsolete. As another poster points out you can buy a ready made max232 chip RS232 to TTL converter for less than three quid. Be sure it's 3.3v on the TTL side. You don't want to fry your calculator.

The CH340G chip is a fairly new, very cheap, USB to TTL converter. It gives you the option to set TTL levels at 3.3v or 5v. We want 3.3v (wouldn't 5vTTL to USB just be a passive cable?). You can buy a ready built circuit on a USB plug for a quid, thats less than two dollars. All you need to add is a 2.5mm stereo jack plug and a bit of heat shrink tubing. Three solder joints total.

Makes sense to me.

Anthony.

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Here is an example

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Here is an example of the right six pin board

Lookat this on eBay http://www.ebay.co.uk/itm/272674673389

Don't get one of the five pin ones. They break out the 3.3v and 5v pins but just for powering external devices. They don't break out the VCC pin you need to jumper the desired operating voltage to.

The tip of the stereo jack is transmit, the next band is receive and the big bit at the base is ground.

Take any cheap 2.5mm stereo jack lead and cut the other end free to make three solder joints to the board or solder little pin sockets to them so you can plug on. Using a ready bought lead can get you a smaller form factor than buying a jack plug to solder. This then fits the calc port more easily. If you can find one with nice ferrite cores all the better. An actual Casio to Casio lead is only two or three quid with postage now now but if you're like me you prolly have a bunch of old leads you can cannibalise.

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You'll need to install the ch340 drivers before the Casio software. Make sure the pc has the port set at a single digit location and then install the Casio software. People seemed to favour the 122 version over the 123 version and there is a 124 version as well now.

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My techie friend assures me that any cable between USB and TTL would have to be active as the USB port relies on an 'intelligent' chip to identify itself and negotiate communication. Hence chips like the 340 having a five volt TTL mode. Just wanted to update. Still waiting for the two chips I bought to arrive. May update once I have played with them.