Post by thread:[PICLIST] [EE] 3V i2c screen control

I have to interface some i2c based moble telephone lcd displays to some pic16f84s. However the operating voltages of the screens are 3Volt. I have not tested the lcds yet, but am I correct in thinking that the i2c will still be running at 5v or will it be at 3v. Also, if the i2c is at 3V does anyone have know of a suitable bi-directional buffer for i2c to convert the data and clock to 3v from 5v and vice versa. I saw a buffer type interface before which did a similar job before to let the i2c bus travel long distances over cables. Another possibility might be to run the pic at a lower voltage, but there will be other components driven by it, including an RS232 serial line driver which must have 5v as it generates +10 and -10 from the 5v supply current. The circuit must be very reliable, so I don't really want to chance driving the rx and tx to the serial driver at 3v if poss. Any suggestions ? -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

For the I2C interface check the Philips I2C specification document on their website. It shows level conversion being done with just 2 FET's. I have not done it but others have reported on this list that it is really that simple to do >Another possibility might be to run the PIC at a lower voltage, but there >will be other components driven by it, including an RS232 serial line driver >which must have 5v as it generates +10 and -10 from the 5v supply current. Use the MAX3232E as the RS232 converter. It will operate from 3V and give the +/-10V out. Then your only problem is to see if the PIC will work at a fast enough clock rate when run on 3V. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

> I have to interface some i2c based moble telephone lcd displays to some > pic16f84s. However the operating voltages of the screens are 3Volt. I have > not tested the lcds yet, but am I correct in thinking that the i2c will > still be running at 5v or will it be at 3v. Check it now! Most probably it runs at 3v. > Another possibility might be to run the pic at a lower voltage, but there > will be other components driven by it, including an RS232 serial line driver > which must have 5v as it generates +10 and -10 from the 5v supply current. Use a MAX3232 or similar. When your circuit is as it appears - consist only of PIC, LCD, RS232 and few minor components, it is really best & easiest to use whatever voltage the LCD requires. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use listservKILLspammitvma.mit.edu?body=SET%20PICList%20DIGEST>

If you go to www-us.semiconductors.philips.com/i2c/facts/#levelshifting it shows you how to interface 5volt and 3.3volt i2c busses together just using a couple of fets regards Chris Carr {Original Message removed}