USB on cheap MCU

Is it possible to add low speed USB to an MCU which doesn't have USB? From what I read, it looks like it wouldn't be all that difficult. The reason I ask, is USB adds a few dollars (in single quantity, so probably 70 cents or so in high quantity) to the price of a MCU. It is very important to reduce cost as much as possible.

Tony

It is, see v-usb (formerly avr-usb) to add usb to various avr chips, but whether there's space for the usb and reprap firmware is another matter. By all means try, I'd certainly prefer a more native usb interface.

Where i work we use the FTDI USB/Serial chips to add USB connections to smaller controllers without USB interface.
I'm not shure tho if this is what you're looking for. The idea is to only use the USB as physical connection and having a virtual COM port on the computer and basically use the same communications as for an RS232 connection. The main reason we do this is because a lot of our older software and hardware still only supports RS232 communications, but modern computers (laptops) don't have the RS232 interface anymore. So, we are basically using the FTDI chips to make our own adapters.

If you have a free UART on your microcontroller it is pretty easy to implement them in your design. We mainly use the FTDI FT232R chip. Single unit price is quite high with 4.50$ tho, so we really only use them if we have to. (I think we have them listed for ~2$ in our companys stock)

For new products we try to directly use controllers with an usb interface now, as this is usally cheaper, smaller and easyer to implement.

Btw, this is only for usb slaves. Adding host functions with an FTDI chip would need quite some more expensive chips. (If you were thinking about using usb-flash drives directly from your microcontroller, as an example)

Cheapest way to add USB to a non USB controler or device could well be:-

[dev.forums.reprap.org]

Cheers

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

That v-usb info was quite helpful, thanks! I probably won't be using an AVR chip, but I'm sure I can use the info to figure out what I need to do.

I didn't find anything cheap in that last link. When I say cheap, I'm talking cheap in half a million quantities. I have to seriously nitpick to get this thing as cheap as possible. The FTDI FT232R chip is almost more expensive than all my electronics combined... At least that's what I'm trying for.

That max232 chip for $1 though might be useful info. I can't afford it, but... I might put it on the circuit board so a person can solder the components on if they need RS232. Not sure. I wonder how common it is that people in very poor countries have computers without USB.

Tony

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Creating the society of the future
[conceivia.com]

Hi Ant

If you port the soft USB port to another micro you will need to be very careful because the timing is tight. You will almost certainly have to code in assembler.

Also, you may face some nasty timing issues: you will be trying to run three stepper motors & an extruder in real time (violate this and build quality goes down) and USB in real time (violate this and comms drop out). It may simply not be possible...

A reasonable micro (Atmel AVR (8 bit), Microchip PIC18 (8 bit) or Texas Instruments MSP430 (16 bit)) with USB device support seems to be about $2 to $4 each as listed on manufacuter's websites. Issues such as pin count and memory seem to impact the price heavily - the marginal price of USB doesn't seem to be huge. If you need real USB this may be the cheapest way to get it.

If you are serious about 500,000+ quantities, an ASIC may actually prove to be the cheapest option - you could get the micro, USB core, stepper drive logic (but probably not power transistors) etc. into one chip. In a multi-chip solution you may end up paying literally dollars just for the packaging! Of course, the problem with ASIC design is the stratospheric non recoverable engineering charges.

Good luck
jbb

The main thing which everyone look on a computer equipement is it's quality.
So price can be cheap but the product must have to be excellent.

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Personal Loans with No Credit Check

Quality is almost purely a factor of design, and has almost nothing to do with the price of the components.

I'm moving away from the idea of this product being open source. The problem with open source, is it prevents profit, which also prevents investment. If I can make a little profit, I can get investors and make it cheaper, and the profits can then go toward creating open source CAD and CAM software.

I feel it is very important to get some decent 3D CAD and CAM software and also electronic design software that are freeware. I feel that is more important than having this project open source.

I think if I go with closed source, the selling price will be just as cheap, because of the ability to get investment, but the profits will be enough to create some pretty nice freeware open source 3D CAD/CAM and electronics software. In fact, I think it'll even make the selling price cheaper.

Tony