Help With College project - Comms Level Shift

[Kirky]

I am working on my college project in which I need to perform a level shift
but am unsure where to start.

The levels are as follows


Unit 1 Unit 2

Logic 0 -0.6v 0v
Logic 1 +5 to +6 2.5 to 4.1v

Unit 2 Unit 1

Logic 0 0 to 0.3v 0 to 0.8v
Logic 1 +0.7v to 3.3v 0.7v(min 0.5mA)

The Supply voltage I am working from is 3.6v.

Any help would be much appreciated.

 

[Jim Thompson]

I am working on my college project in which I need to perform a level shift
but am unsure where to start.

The levels are as follows


Unit 1 Unit 2

Logic 0 -0.6v 0v
Logic 1 +5 to +6 2.5 to 4.1v

Unit 2 Unit 1

Logic 0 0 to 0.3v 0 to 0.8v
Logic 1 +0.7v to 3.3v 0.7v(min 0.5mA)

The Supply voltage I am working from is 3.6v.

Any help would be much appreciated.

Which ones are SENDING levels, and which are RECEIVING? And provide
some information about source impedances, loading impedances and speed
required.

...Jim Thompson

 

[Kirky]

Baud Rate is 1200, Unit 1 is a Data Logger which we use at work which has
OPTO coupled comms lines and Unit 2 is a National Semiconducter LMX9820
Blue-Tooth serial port module.

Sorry for being vague but im a novice at the moment. Ive got the datasheet
for the LMX9820 but am unsure as to what the impedances are.

Unit 1(S) to Unit 2(R)

Logic 0 -0.6v 0v
Logic 1 +5 to +6 2.5 to 4.1v

Unit 2(S) to Unit 1(R)

Logic 0 0 to 0.3v 0 to 0.8v
Logic 1 +0.7v to 3.3v 0.7v(min 0.5mA)

In each case the Sending(S) voltage needs to be converted to the received(R)
voltage.

 

[Fred Bloggs]

Baud Rate is 1200, Unit 1 is a Data Logger which we use at work which has
OPTO coupled comms lines and Unit 2 is a National Semiconducter LMX9820
Blue-Tooth serial port module.

Sorry for being vague but im a novice at the moment. Ive got the datasheet
for the LMX9820 but am unsure as to what the impedances are.

Unit 1(S) to Unit 2(R)

Logic 0 -0.6v 0v
Logic 1 +5 to +6 2.5 to 4.1v

Unit 2(S) to Unit 1(R)

Logic 0 0 to 0.3v 0 to 0.8v
Logic 1 +0.7v to 3.3v 0.7v(min 0.5mA)

Unit 1(R) Logic 1 makes no sense- you say 0.7V?

 

[Kirky]

sorry my mistake, that should be 2v.

 

[Fred Bloggs]

sorry my mistake, that should be 2v.

First off, the minimum baud rate on the LMX9820 is 2400 baud-
you might want check for compatibility with your data logger. From your
specs, the data logger appears to be running off Vcc=5V, and the
Bluetooth interface is running off 3.6V. The Bluetooth receive looks to
be CMOS leakage only- it will not load your data logger at all. You will
need to reduce the data logger drive to the LMX9820 UART_RX/ _CTS pins.
The LMX9820 Vih threshold is 0.7 x IOVCC, so that if IOVCC is 3.6V, this
means a minimum input of 2.5V. The Vil is 0.2xIOVCC or 0.72V maximum.
You can run the UART_TX and _RTS pins of the LMX9820 directly to the
data logger. Something like this should work, the diodes should be BAS
Schottky types- they come dual in little SOT packages:
View in a fixed-width font such as Courier.




IOVCC >------+
|
[10K]
|
UART_RX <-----+--|>|--[100]--<
|
|
LMX9820 SIDE GND--|>|-+
FROM DATA LOGGER


IOVCC >------+
|
[10K]
|
UART_CTS <-----+--|>|---[100]--<
|
|
GND--|>|-+




IOVCC---|<|-+
|
|
UART_TX >------+-[100]--------->
| TO DATA LOGGER
|
|
GND--|>|-+




IOVCC---|<|-+
|
UART_RTS>------+-[100]--------->
|
|
|
GND--|>|-+

 

[Kirky]

thanks for that, much appriciated.

sorry my mistake, that should be 2v.

First off, the minimum baud rate on the LMX9820 is 2400 baud-
you might want check for compatibility with your data logger. From your
specs, the data logger appears to be running off Vcc=5V, and the
Bluetooth interface is running off 3.6V. The Bluetooth receive looks to
be CMOS leakage only- it will not load your data logger at all. You will
need to reduce the data logger drive to the LMX9820 UART_RX/ _CTS pins.
The LMX9820 Vih threshold is 0.7 x IOVCC, so that if IOVCC is 3.6V, this
means a minimum input of 2.5V. The Vil is 0.2xIOVCC or 0.72V maximum.
You can run the UART_TX and _RTS pins of the LMX9820 directly to the
data logger. Something like this should work, the diodes should be BAS
Schottky types- they come dual in little SOT packages:
View in a fixed-width font such as Courier.




IOVCC >------+
|
[10K]
|
UART_RX <-----+--|>|--[100]--<
|
|
LMX9820 SIDE GND--|>|-+
FROM DATA LOGGER


IOVCC >------+
|
[10K]
|
UART_CTS <-----+--|>|---[100]--<
|
|
GND--|>|-+




IOVCC---|<|-+
|
|
UART_TX >------+-[100]--------->
| TO DATA LOGGER
|
|
GND--|>|-+




IOVCC---|<|-+
|
UART_RTS>------+-[100]--------->
|
|
|
GND--|>|-+