interfacing ibutton to PC using USB

[konzen]

Hey guys,

Part of my final year project requires interfacing an ibutton to a embedded computer to serve as a user authentication feature.

My supervisor has handed me two things, namely;

a) ibutton ,model: DS1990A which is an ID only ibutton
b) ibutton reader, model: DS9092 which is has two wires coming out(1 for power and one for data(ibuttons use the 1-wire interface))

My question is, can I interface the ibutton reader to a PC using the USB interface? There are USB adapters for sale which is a basically a reader with a built in USB connector. However, I would like to construct one on my own.

Since the ibutton model only allows reading, can I just connect the data wire of the reader to the data pin of the USB jack and forget about the write pin on the USB connector. If I connect the power wire on the ibutton reader to the USB Vcc, where do I connect to USB ground to?

Has anyone done this? Thanks in advance folks

 

[Jay.slovak]

Hi,

Maxim produces exactly what you need, an USB interfaced 1wire/iButton reader, complete with Java source code. Check out the datasheet **broken link removed** . Note that you can also build this adapter from scratch, the DS2490 IC is handing everything.

Jay.

 

[konzen]

I'm aware of the USB adapter maxim is offering. however, I want to utilize the reader that I have with me right now. I have the appropriate hardware to read the ibutton but I just need advice on how to build an intermediate USB connector between the reader and the PC.

To make things clearer the reader that I have now with me is the DS9092 model as shown on this page. It has two wires coming out of it.

**broken link removed**

Can this be done? thank you.

 

[Jay.slovak]

That's not a reader, but only a mechanical iButton holder, which could be connected to the reader I pointed in my previous post. The 'reader' what you have only provides you access to the 1wire bus (you can't solder wires on the iButton).

 

[konzen]

Thanks. I'm gonna do more reading. Anyway have you ever developed an ibutton interface before?

 

[blueroomelectronics]

Many of us have, it's not that difficult. DalSemi has plenty of application notes.

 

[Jay.slovak]

Actually yes I have.

I used DS1402D-DR8 (iButton holder) and connected it via RJ-12 jack to a USB reader based on DS2490. The datasheet of DS2490 has a reference schematic that I used. It is a very simple design, but works great. The Software is free directly from Maxim.

 

[konzen]

I see.

So do you guys suggest that I obtain an adapter like you did? Or is there a way to do it with the existing probe that I have?

 

[blueroomelectronics]

You need the adapter. The probe you have contains no electronics and is meant to attach to a microcontroller or adapter.

 

[Jay.slovak]

You can use the probe you already have, it's the reader that you should be concerned about.

 

[konzen]

Cool. My supervisor did tell me to use a microcontroller to read the ibutton. But obtaining the microcontroller and learning how to use it requires time. So right now I'm trying to find ways of directly connecting it to the embedded computer. Guess I should get an adapter then. However, I did read somewhere on the maxim site that I could let the software handle all the reading and all I need is just a simple circuit with a pull up resistor. I might be giving that a shot.

 

[blueroomelectronics]

You can toggle an I/O pin to read an iButton. But that may not be as easy as you may think. The iButtons are very timing sensitive.

 

[Jay.slovak]

I suggest you first learn what an iButton is: **broken link removed**

 

[konzen]

I thought of doing that too but then apparently it's quite difficult lol.

Yeah I've gone through quite abit on ibuttons and I roughly know what it does. Just wanna find out alternatives methods of interfacing the ibutton.

Thanks abunch

 

[Jay.slovak]

I would suggest to use the Serial Port, and not USB. Embedded computers still have them. And it is much easier this way.

Have a look at **broken link removed** (notice the schematic diagram in the datasheet).

Jay.

 

[konzen]

Agreed. Since I have the probe, I think I'll be using this schematic which is almost the same as the one in the link you gave me. Should be good right?

 

[Jay.slovak]

That's a good general idea. Now you only have to fine tune the schematic (add some capacitors and a way how to power the circuit) write the software and you are ready to go.

 

[blueroomelectronics]

Just build the circuit in the DS9097U-S09 datasheet.

 

[konzen]

Thanks for your comments. As blueroomelectronics suggested, I would construct the circuit shown on the datasheet. However, I've been reading up on the literature on how to read/write a 1-wire device through serial ports and I've come across the name UART many times. I'm a little confused as that piece of literature emphasizes on the use of a UART chip but the data sheet schematics show no sign of a UART chip in there.

What are your opinions?

For reference here's the link to it
https://www.electro-tech-online.com/custompdfs/2008/05/AN74.pdf

 

[Jay.slovak]

UART is a part of MCU or PC, it is not essential but it simplifies writting the Software. It's a hardware unit that takes care of low level serial operations.