2009年10月Circuit Cellar电子杂志：信号处理与工业以太网解决方案

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"Circuit Cellar No.231 - October 2009 (Malestrom)" 是一本电子书，属于《电路窖》杂志的一期，专注于计算机应用，内容涵盖信号处理、红外信号控制、电力网频率监测、电容ESR测量、数字控制放大器设计等多个领域。在这期杂志中，读者可以深入学习各种复杂信号处理问题的解决策略。例如，"Tackle Difficult Signal-Processing Problems"一文可能详细讨论了如何应对在信号处理过程中遇到的各种挑战，包括噪声过滤、信号恢复和信号分析等技术。 "IR Signal Control Made Simple"这一主题则可能介绍了如何简化红外信号的控制，这在远程控制、自动化和无线通信系统中非常常见。文章可能涵盖了红外通信的基本原理、编码解码方法以及如何设计和实现简单的红外控制系统。关于"Power Grid Frequency Monitoring"，文章可能会探讨电力系统的频率监测技术，这对于电力稳定性和能源管理至关重要。内容可能包括实时监测方法、异常检测以及频率波动对电网的影响。 "Capacitor ESR Measurement Explained"可能会详细解释电容器等效串联电阻（ESR）的测量技术，这是评估电容器质量和寿命的重要参数。文章可能涉及不同的测量工具、方法以及ESR值对电路性能的影响。 "Digitally Controlled Amp Design"部分则可能探讨数字控制放大器的设计，这是一个现代电子设计中的关键元素。话题可能包括数字信号处理器（DSP）的应用、闭环控制算法以及如何优化放大器的性能和精度。此外，杂志还可能包含其他实用电路设计和嵌入式系统应用的文章，如"Low Cost Solution for Industrial Serial to Ethernet with Digital I/O and Analog to Digital Converters"，这部分可能介绍了一种经济实惠的工业串行到以太网转换解决方案，它带有数字输入/输出和模数转换器功能，适合于自动化和远程监控应用。产品信息提供了NetBurner的SBL2e硬件和软件解决方案，包括其硬件特性（如耐高温、接口兼容性）和软件特性（如网络通信协议支持、远程控制能力），为读者展示了如何实现这样的系统集成。这期《电路窖》杂志提供了一个丰富的学习平台，涵盖了广泛的电子工程和计算机应用知识，无论是对业余爱好者还是专业工程师来说，都是不可多得的参考资料。

CIRCUIT CELLAR

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October 2009 – Issue 231

the IR learning and sending routines,

as well as to implement the code

needed for the DNS, POP3, and

SMTP software components.

from the same telnet session. If you

forget it, you can reset it by pressing

the button for more than 5 s.

The IR command setup to power-

up the AC is also simple. Pressing

the Mode button once puts the

ACcontrol in IR learning mode. The

infrared command is then “learned”

by pointing the original AC remote

control to the IR-receiving sensor

and pushing the Power button on the

remote. The LED indicator remains

on while learning mode is activated.

HARDWARE DESIGN

The WIZnet module simplified the

design. In addition to the WIZ810MJ

module and the dsPIC30F4012

microcontroller, I used a Vishay

Intertechnology TSOP321 38-kHz IR

receiver module and a TSAL7400

high-output IR emitting diode (see

Figure 2). The WIZnet module com-

prises everything needed for the Ether-

net interface, including the RJ-45

socket, the support circuit, and a SPI. I

chose the dsPIC30F4012 for its RAM,

EEPROM, flash memory, and timer

resources. I needed it to implement

The dsPIC software handles the

higher-level TCP protocols, all the

communication with the W5100, the

user interface, and the IR lear n and

Figure 3—

The segmented software makes it easy to develop and understand. The initializa-

tion process is straightforward. The rest of the code is an event loop, where an action is

taken after a specific event is detected.

Initialize

microcontroller

ports and timers

Reset and

initialize

WIZnet

W5100

Restore IPs and

other parameters

from EEPROM

Initialize

telnet

interface

Push button

pressed?

Setup

mode

Process

telnet

Check POP3

e-mails

Data in

telnet

port

POP3

Polling?

Start

Yes

Figure 2—

I used a hardwired TCP/IP hardware module and a SPI. It seems as though the software in the dsPIC30F4012 handles everything.

But in reality, most of the TCP/IP complexity is hidden from the programmer in the W5100 IC located inside the WIZ810MJ module. A single

3.3-V regulated power source rated at 350 mA is enough to power this project.

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CIRCUIT CELLAR

October 2009 – Issue 231

send functions. It controls the

WIZ810MJ module through a four-pin

SPI and a fifth pin for a RESET signal.

I manually coded the SPI routines

because the hardware SPI module

shared the pins with the PIC debug-

ging interface. The 38-kHz infrared

module handles the IR code recep-

tion and sends a filtered signal to the

dsPIC30F4012’s CN3 input config-

ured to generate an interrupt when

the logic state changes. Finally, the

dsPIC30F4012 is also connected

through the RE0 pin to an IR LED

through a 2N3904 amplifier. The

RE0 is driven by the dsPIC PWM

module set to generate the required

IR frequency of 38 kHz. The only

other two connections are for the

push button and red LED as the user

interface.

SIMPLE SOFTWARE?

The hardware is simple, but is the

software complex? No. If you’re famil-

iar with the TCP protocols (i.e., the

POP3, DNS and SMTP protocols),

the only complexity that remains is

related to the W5100 interface and

IR-handling routines. Let’s review

each software segment and see how

they work, so that you can form your

own conclusions about this project’s

complexity. I encourage you to

download the source code from the

Circuit Cellar FTP site so you can

follow the subsequent explanations.

Figure 3 depicts the software flow.

You can see the standard hardware

initialization that covers the dsPIC

resources and the W5100 chip. It is

followed by the parameter initializa-

tion in the EEPROMs and the initial-

ization of the telnet interface. The

software then enters in a loop to

look for the push button or data in

the telnet port or data in the POP3

account. Each of these functions is

handled in a separate code segment.

This flow is shown as the main()

routine (see Listing 1).

The first four routines initialize

the system. The init() routine ini-

tializes the dsPIC30F4012 by config-

uring the I/O pins, programming the

PWM module to the output IR fre-

quency, sending and holding the

RESET signal to the WIZnet module,

and programming the systick timer

used for the delay routines. The next

initialization routine is for the IR

system, IR_init(). This initializes

the IR input port interrupt and the

Timer3 module (TMR3) to count

every 8.7-µs resolution used to meas-

ure the IR pulses. When I cover the

IR routines later in this article,

you’ll see that these can easil y cope

with most of the IR p rotocols.

After setting up the IR hardware,

the next thing to do is to prepare the

W5100 hardware TCP/IP chip. This

is done with the reset_w5100 and

sysinit calls. The former just resets

the W5100. It is held in reset by the

init() call, so in this second call it

just frees it after the required hardware

reset delay of more than 10 ms. A

software reset command is then sent

to the chip itself. Then comes the

sysinit call, part of the W5100

driver, which configures the trans-

mit and receive buffer sizes. The

W5100 has four channels, each for

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October 2009 – Issue 231

different TCP/IP connections. Also,

the W5100 has 8 KB of internal

memory. The amount of memory

you assign to each channel depends

on the simultaneously open sockets

or connections in your software,

which will determine the volume of

traffic the system can handle. More

memory assigned to a channel means

that the software may be slower

when attending the connection as

the buffer is bigger and data will not

be lost.

I used three channels, so I config-

ured the W5100 in the only possible

configuration: 1 KB for each transmit

and receive buffer for four channels

(8 KB in total). Thus, packets can’t

exceed the 1 KB size, which is not a

problem for my configuration. In my

software, channel 0 is assigned as an

administration RAW port for IP

address configuration, channel 1 is

shared for the DNS and e-mail proto-

cols, and channel 2 is for the telnet

TCP interface. Channel 3 is reserved

as a UDP socket for broadcasting the

message to other receiving modules

for future expansion.

Once the hardware is ready, the

main code restores the IP parameters

from the EEPROM, sets the fixed

hardware MAC address, and initial-

izes the IP values in the W5100 chip.

It is important to note that the

W5100 chips don’t come with MAC

addresses. You can purchase them

separately at www.ieee.org, as noted

on WIZnet’s FAQ page. I created one

for this demo, but please note that

you need to obtain legal MAC

addresses to be able to commercial-

ize products with these chips. For

the demonstration’s sake, I just had

to be sure that the selected MAC

address didn’t match any other MAC

address in my lab.

Listing 1—

After initialization, a simple loop is used to check for three dif ferent events: a

push button press, data in the telnet port, or a POP3 e-mail trigger .

// ----- main program -------------------------------------------/

int main()

{

// initialize microcontroller

init();

// initialize IR system

IR_init();

// reset w5100

reset_w5100();

// initialize w5100

sysinit(0x00, 0x00);

// initialize MAC/IP layer with default values

restore_parameters(); // restore parameters from EEPROM

setSHAR(my_mac); // set MAC address

init_ip(); // init IP values

// initialize telnet port

init_telnet();

// process cycle

systick = 0;

for (;;) {

// check if setup mode is requested

if (PUSH_BUTTON == 1)

setup_mode();

// check if telnet session

if (getSn_SR(SOCKET_TELNET) == SOCK_ESTABLISHED)

process_telnet();

if (email_hostname[0] && systick >= email_freq)

email_process();

}

return 0;

}

Photo 3—

The sample Linux set-up utility

receives the following: the broadcast

address of the PC and the MAC address of

the device, the desired IP, the netmask, the

gateway, and the DNS addresses. A UDP

packet is broadcast addressed to port 9000,

and it’s captured by the ACcontrol’s Raw

mode, even if its IP doesn’t belong to the

current network.

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CIRCUIT CELLAR

October 2009 – Issue 231

The W5100’s IP setup procedure is

very simple, as you can se e in the

init_ip routine. I first set the IP

address by calling the W5100 driver

setSIPR routine. The netmask is

set with the setSUBR call and the

gateway address configuration

requires a call to the setGAR rou-

tine. Each IP address and netm ask is

represented as a 4-byte array. The

DNS address is saved in a local vari-

able in the format required by the

DNS search routines.

Finally, the initialization segment is

completed by a call to the Telnet ini-

tialization routine, init_telnet().

It opens a TCP socket in the

W5100’s preassigned SOCKET_TEL-

NET channel and sets it to lis ten

mode. Please note that these calls

are non-blocking. They just set th e

socket to listen. The actual packet

“listening” is performed in the

process_telnet segment code

where the socket is tested for data. If

you are familiar with the sock et

interface, you will realize that the

WIZnet driver interface is similar to

other operating systems like Unix.

Some differences exist. In the cu r-

rent implementation, the program-

mer has to first check that there is

data in a socket before callin g the

socket read routine (i.e., there is no

select call and the read routines are

non-blocking). This is needed

because you don’t want to stop the

CPU waiting for a packet to ar rive.

You check for data, and if there is no

data just continue to check other

things. This technique is used a lot

in embedded processing and avoids

the need for a multitasking RTOS.

PROCESSING LOOP & SETUP

Refer to the main routine (see

Listing 1). After initialization, the

code is a simple loop th at checks for

a button press, a new connection to

the telnet socket, or a received trig-

ger e-mail. Each event produces a

call to a corresponding routine. A

button press event puts the device in

set-up mode via the setup_mode

routine. A new telnet connection

executes the process_telnet code,

which implements the telnet inter-

face. Finally, if a new e-mail is

detected, the email_process rou-

tine activates the IR signal and sends

you a reply e-mail.

Pressing the Set-Up mode push

button activates the set-up routine.

This makes the ACcontrol listen to

a special UDP packet sent from a PC

program that’s designed to send the

device IP configuration. In Set-Up

mode, you execute a simple program

to request the IP address, netmask,

default gateway, and DNS IP and

then send it to the network. But how

can the ACcontrol, with no defined IP

configuration, receive an IP packet?

Other devices on the market generally

use DHCP or a fixed IP address for

the initial contact. DHCP was unde-

sirable for this case because it would

be difficult for you or the set-up pro-

gram to know the IP address

required for the rest of the configura-

tion. A fixed IP would force you to

change the PC’s IP to be able to com-

municate with the newly reset

device. Thus, I decided to use another

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October 2009 – Issue 231

approach and experiment with the

W5100 chip’s Raw Socket mode.

Set-Up mode opens a socket in

Raw mode. If you are u nfamiliar

with Raw Socket mode, think of it as

a “promiscuous” (as it is called in

some circles) Ethernet interface that

captures every packet, even if it isn’t

directed to the device. In this mode, I

checked for a specific UDP packet

sent from the PC with the required IP

configuration. When the ACcontrol

sees it, it takes the infor mation from

the UDP packet body and sets itself

accordingly. The previous IP configu-

ration doesn’t matter because this

method always works (see Photo 3).

The setup_mode routine implements

this as well as the IR lear ning and

password reset functions.

For the IP configuration, there i s a

do-while loop in the code that

checks for a packet arrival. It checks

that it is an IP packet (0800 hex at the

Ethernet-type field). Then it checks if

it is a UDP packet directed to por t

9000 and if the packet is a special

packet sensed by a magic number in

Listing 2—

The IR_send routine just replays the sampled transitions from the IR learn-

ing routine. The ir_array contains the elapsed time between changes of the learned

signal. If a signal must be modulated at 38 kHz for the duration of the transition, the

most significant bit of the word is set to one.

// send the learned IR command

void IR_send(void)

{

uint8 i, logic;

uint16 t;

for (i = 0; i < ir_transitions; ++i) {

t = ir_times[i]; // get time

logic = (t&0x8000)?1:0; // get logic

IRpulse(logic, (t&0x7FFF)); // send pulse

of the corresponding logic

}

// wait lead time

IRpulse(0, 2298);

}

its first data position. If everything is

fine, the configuration is extracted

from the packet, applied to the sys-

tem, and the Set-Up mode is exited.

INFRARED COMMANDS

Most of the IR commands for

remote control consist of a pulse-

modulated 30- to 60-kHz signal.

(Note that 38 kHz is the most com-

mon.) Although different protocols

exist for embedding a command in

the signal, what I wanted was just to

learn a single command—the power

On/Off signal—and then be able to

replay it when needed. The sys tem

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