CAN to Analog Converter

SD0707Shefali DhakaJosh SchroederDan Williams

Introduction

Client: Sauer-Danfoss Client Representative: Lincoln Davidson Faculty Advisor: Dr. Nelson

Introduction

Device reads CAN messages Uses the CAN data to generate an analog output The arbitration ID of the CAN component will

determine how the message is interpreted User configures

Output Range (between -5 and 5 volts) Data Type of message Bit Order (Intel, Motorola)

Digital Hardware Requirements

We are to use components that Sauer-Danfoss uses in their own designs whenever possible

A microcontroller will be used to accept and interpret CAN messages

The micro must be able to communicate over RS232 for debugging

The micro must have access to a large amount of memory

DAC must have 16 bits of resolution

Software Requirements

Labview will be used to create a configuration program capable of changing how the CAN message is to be interpreted.

The user should be able to save new configurations of how the message is interpreted

The software on the microcontroller will be programmed through CAN

New user configurations will be retained after a power cycle

Generating a Variable Range Output Two methods emerged

Method 1: Use a DAC with constant output range, and vary the offset and gain

Method 2: Vary the output range of the DAC and use a constant offset and gain.

Generating a Variable Range Output Method 1

Two digital potentiometers could be used in a differential op-amp circuit

One to adjust the offsetThe other to adjust the gain

Method 2An extra 16 bit DAC could be used to adjust

VREFH & VREFL creating a variable output range

Generating a Variable Range Output Method 1: Advantages

Cost: Dual digital potentiometers prices range from about 1 to 5 dollars

Reduce the number of components Method 1: Disadvantages

Low number of distinct stages (usually 256)Not a component Sauer-Danfoss uses

Generating a Variable Range Output Method 2: Advantages

Has high resolution (16 bits)Can use parts Sauer-Danfoss typically usesReduces software complexity

Method 2: DisadvantagesCost: $12 per chip

Generating a Variable Range Output We chose Method 2

The higher resolution allows us to better match the users specifications

Reduces the complexity of the analog circuitryCan use Sauer-Danfoss partsWe were advised that digital potentiometers

can be unreliable

Generating a Variable Range Output Use the DAC8554 with SPI Output equation

VOUT = (Din/65535)*(VREFH - VREFL) + 2VREFL

The output range is anywhere between 0 and 2.5 volts

Minimum output is 2VREFL => Max VREFL = 1.25 V

Maximum output is VREFH + VREFL => Max VREFH = 2.5 V

Generating a Variable Range Output Design uses 5V and 0V as our VREFH & VREFL for

our first DAC Problem: only a small amount of the 1st DAC’s

resolution is used

DAC

VREFH

VREFL

VOUTA

VOUTB

DAC

VREFH

VREFL

VOUTA

5V(0…2.5V)(0…2.5V)

(0…1.25V)

VrefH vs. VrefL

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5

VrefL

Vre

fH

Generating a Variable Range Output

Generating a Variable Range Output Solution: use voltage dividers to the reduce the

output voltage

DAC

VREFH

VREFL

VOUTA

VOUTBDAC

VREFH

VREFL

VOUTA

5V

(0…2.5V)(0…2.5V)

(0…1.25V)

R

R

R

3R

(0…5V)

(0…5V)

Digital Components

PIC24 was chosen as our microprocessor Bootloader and other code from Sauer-Danfoss can be

used EEPROM with I2C interface stores user

configuration data RS232 transceiver allows for debugging CAN transceiver

Programming PIC Receiving user configurations Receiving digital messages to convert to analog

Digital Components

Digital Components

Software

User Configuration Data File

Each CAN component must have a configuration file stored in the EEPROM

User Configuration Data File

Value # of bits

Component ID 29

Max Analog Out 16

Min Analog Out 16

Max Digital In 64

Min Digital In 64

Data Type (signed/unsigned int, float) 2

Message Bit Order 384

Total 575

Once the input CAN signal that was digital has been converted to analog, it has to be amplified and converted back to a differential signal.

The circuit can be divided into 2 parts: Part 1 to amplify the DAC output.

Part 2 to provide protection from undesired supply.

Requirements: For part 1:

An Inverting operational amplifier. resistors.

For part 2: 2 Inverting operational amplifiers. resistors. PTC (Positive Temperature Coefficient) Diodes Transistors PTC (Positive Temperature Coefficient)

Low noise op-amps were required for obvious reasons. Quad op-amps so there are easy and clean connections

on the PCB. High Gain bandwidth product. Low input offset voltage: It is a direct DC error. Low equivalent input noise voltage :

Noise = (input noise voltage)* (bandwidth)^1/2; So, it is very important to keep this low. Slew rate: to stabilize our output from the op-amp, a low

slew rate was desired(somewhere around a 50V/ms) Low offset voltage High temperature range: -40 to 85 degree Celsius for

use in any environment. High common mode rejection ratio: about 90-100 dB High open loop gain: It ensures higher DC accuracy.

Part 1: So this op amp will be used to amplify the

signal coming in from the D2A (VD2A) to a 5V as per the following equation:

Vout= 4 * (VD2A -1.25) This op amp1 is only used to generate the

desired output and supply it to the next two circuits that provide the protection (Part 2 ).

We decided on using an Inverting amplifier.Why? Because it has a negative feedback which is

good as positive feedback tends to increase oscillation effects.

Input the DAC output at the negative of the op amp to stabilize the inputs.

Resistor values R5 : R7 = 1 : 4

Thus, we get the negative output which is further fed into part 2.

Having some sort of safety provided between the op amp and the point where any voltage can be applied by the user is extremely important as then we have a secure device which is not prone to failures pertaining to accidental mistakes made by the user.

Put in a fuse:

Problem: Fuse would blow off and the user will have to take

the pain of changing the fuse.

High load Large resistance used.

Will affect the current.

Use a PTC: PTC stands for Positive Temperature

Coefficient. Materials whose resistance increases

when their temperature increases which happens when a high voltage difference is applied across them.

The greater the coefficient, greater the increase in the resistance offered.

We use a 27 ohm PTC as that is what is used by Sauer Danfoss.

Problem: This is good and can be used but its increase in

resistance might not keep up if the applied voltage is extremely high.

So, we put a PTC instead of the normal resistance that was shown in the previous schematic, this reduces the current flowing through it to an extent and now we can have something else added so the remaining current is drained to someplace instead of going into the op amp.

Diodes All the current into+/-12V

might not take such high current

Match not only the ratio of resistances at both the positive and the negative pins of the op-amp but try matching their values also; sometimes under high voltages this induces some oscillations in the output of the op-amp.

Equations used: Op-amp equation: Vout = Gain (Vd2a - Voffset) Voltage divider: Vout = (R1/R2)*gain

Power Distribution

Power Requirements Power Protection Switching Regulators Switching Inverters Voltage References

Power Requirements

9 to 40 Volt Input Protection against

Battery Reversal Protection from

Voltage Spikes

Voltages Needed1. 12 Volts

2. -12 Volts

3. 5 Volts

4. 5 Volt Reference with 0.1% Accuracy

5. 3.3 Volts

RBO40-40G

Protects against Voltage Spikes Prevents Damage from Battery Reversal Clamps off voltages over 40 Volts Small Size for what it does

RB040-40G

1 2 3

9 – 40 V

NC

1) Input2)NC

3)Output

GND

Vout

LM2596

Input voltages between 9 and 40 Volts 3 Amp Load Current 3.3 Volt Version Over Temperature Shutdown Requires only 4 External Components

RB040-40G

1 2 3

5 3

1

4

2

47K6.8uH

LM25963.3

33E-6HL

6 V

3.3 V

Cout

Cin

NC

L= 33uH L40Cin = 680uF 50V (Panisonic HFQ or

Nichicon PL)Cout= 330uF 6.3V (AVX TPS or

390uF 6.3V Sprague 595D series)

1) Vin2)Output3) GND

4) Feedback5) On/Off

1) Input2)NC

3)Output

GND

LM2731

Fully Adjustable Version Can Boast 3.3 Volts up to 20 Volts Uses small Capacitors and Inductors Small SOT-23 Package 8 External Components

V In

SHDN

SW

FB

LM2731 A = 5VB=3.3 V

6.8uH

40.5K

470pF

13.3K

2.2uF

47K

22uF

GND

1) SW2)GND3)FB

4)SHDN5) Vin

51K

R3

C1

R3

L

R1

R2

Cf

C2

D

Vin

SHDN

SW

FB

6.8uH

117K

270pF 10uF

13.3K

2.2uF

51K

A= 3.3VLM2731

12V

GND

C1

R3

L

D

R1

C2

Cf

R2

1) SW2)GND3)FB

4)SHDN5) Vin

LM2611

Can change 2.7-14 Volts down to -36 Volts Uses input and output inductors to reduce

output ripple Uses two Resistors to control Output Voltage Small SOT-23 Package 9 External Components

LM26115

42

3

1

1) SW2)GND3) NFB4)SHDN

5) Vin

22uH 22uH1uF

1000pF

D22uF29.4K

3.3K

22uF

12V -12V

Cin

Cout

Cff

CcukL1 L2

LM4041

Can supply a Reference voltage up to 15V with better than 0.1% Accuracy

Small SOT-23 Package Uses only three external resistors

12V

1.4K

10K

3K

Lm4041 ADJ

1

2

3

1) FB2) +3) -

RS

R1

R2

5V REF

Future Tasks

Continue troubleshooting design Design and build PCB Write software

C code for PICLabview user configuration

Timeline

Task Desription Duration Start Date End Date

Functional Block Diagram 5 days 1/29/2007 2/2/2007

Gather Componants Lists (ALL) 18 days 2/3/2007 2/27/2007

Design Ideas (All) 44 days? 2/27/2007 4/26/2007

Rough Schematic (All) 20 days 4/1/2007 4/26/2007

Gather Components (All) 8 days 4/27/2007 5/8/2007

Test Components (Josh and Dan) 23 days 5/9/2007 6/8/2007

Break 77 days 5/14/2007 8/28/2007

Design and order Board (Josh and Shefali) 31 days 9/28/2007 11/9/2007

Test Prototype Board (Josh and Shefali) 18 days 9/17/2007 10/10/2007

Software for PIC (Dan and Shefali) 18 days 9/17/2007 10/10/2007

Begin Labview Configuration Program (Dan) 21 days 10/5/2007 11/2/2007

Test Software (Dan) 14 days 11/5/2007 11/22/2007

Test Hardware (Josh and Shefali) 14 days 11/23/2007 12/12/2007

Revisions/Modifications (ALL) 18 days 11/28/2007 12/21/2007

Local ExpensesPart Description Part # Retail Cost Acquired Cost Notes Units/Board Price/Board

CAN Transceiver MCP2551 $ 1.45 $ 1.45   1 $ 1.45

16bit D2A DAC8554 $ 12.00 $ -   2 $ 24.00

EEPROM AT24C512 $ 5.00 $ 5.00   1 $ 5.00

Microcontroller PIC24 $ 18.70 $ 18.70   1 $ 18.70

RS 232 MAX 3223 $ 2.00 $ 2.00   1 $ 2.00

OP AMPS LM741 $ 3.00 $ 3.00 Subject to change 4 $ 12.00

Switching Regulator LM2596 $ 4.70 $ -   1 $ 4.70

Switching Regulator LM2731 $ 3.00 $ -   2 $ 6.00

Power Protection RBO4040-G $ 2.70 $ -   1 $ 2.70

Inverting Switcher LM2611 $ 2.73 $ 2.73   1 $ 2.73

Reference Voltage LM4041 $ 0.62 $ 0.62   1 $ 0.62

Capacitors   $ 1.30 $ 1.30 Subject to change 15 $ 19.50

Inductors L38 $ 2.75 $ 2.75 Subject to change 5 $ 13.75

Diodes MBR0520LT1GOSCT $ 0.25 $ 0.25   3 $ 0.75

Diodes 1N5825 $ 7.50 $ 7.50 Subject to change 3 $ 22.50

Resistors   $ 0.25 $ 0.25 Subject to change 22 $ 5.50

CAN card   $ 500.00 $ - Client Expense 1 $ 500.00

Enclosure   $ 15.00 $ 15.00   1 $ 15.00

PCB Board   $ 100 $ - Client Expense 1 $ 100.00

    Total Price/Board: $ 141.90

    # of Boards: 2

    Total Price: $ 283.80

Budget

Budget

Total Budget Granted by NDSU   $ 200.00

Money Spent   Money Remaining

Component Total   Total

Resistors $ 15.35   $ 184.65

Almost every component we have dealt with we have acquired as free samples

It is hard to project what we will get for free and what we will have to pay for

Summary

We are well on our way to completing the project by the end of next semester.

We have completed a schematic We have run simulations and tested

physical circuits We feel our design is complete and we are

ready to move onto implementation