PLCs/PICs (computer interfacing and controlling)

[g8rpi]

I've been looking into the Avon starter control. Do any of you have the specification for the DC starters you are using? Max current is most important. The only info I can find is on a Hunter conversion by Jet Heritage. That used a 120V DC motor with 10 12V Sealed Lead Acid batteries were the cannon amunition used to go. There is some suspesion that it may actually hve been a 115V AC motor. Brushed motors will run on AC or DC of course.

Robert.

[ernie wrenn]

What type of starter engagement do you have? splined, dog, clutched?

Ernie

[g8rpi]

Hi Ernie,
I don't need a starter, just information on what people are using on their engines. I'm particuarly interested in Avons as these are mostly conversions from cartridge or monofuel starters. I'm assuming that users are concerned that the high starting torque of a shunt wound DC motor can damage the gearbox. Ideal data would be the type, voltage, rated, speed, power, current and duty cycle. Also the and actual current drawn during a start. It would also be interesting to know if the starters have a separate ground return stud isolated from the frame. It is easier to build a low side (ground switching) PWM driver with MOSFETs. This is not possible the the ground return of the motor is through th frame.

Robert.

[stimps]

So im keen to start making something up to control mh engine. I want it to have auto shutdown at overspeed, overtemp, and auto sequence start, control the starter, fuel, gas, monitor rpm and temp, fuel pump ramp up and down speed, and have a couple of push buttons and a simple 16x2 alpha numeric display so i can access these variables to fine tune the startup and throttle response. How do i go about selecting the right PIC to start designing this, or should i simply start writing the logic code and turn it into a program and go from there? I have the pickit 2. Can that prototype devolopment board actually be used itself to create a first working version?

Ive seen the 16f626 chips for sale on ebay and are concerned they are not big enough for the job??

[Richard OConnell]

I started writing my code for the front-end visual display. All the input values will simple update the values of variables in code and what I have already written should take care of the rest. I have it set up to monitor EGTs and RPMs and have multiple levels of warnings and actions to take (like a warning level that awaits user interference, then a danger level where the computer takes over and closes off fuel solenoids). Now all I need is a good addon card, maybe even one that fits in a normal PCI or other expansion slot, that can work with the range of inputs and outputs and I'll add code to listen for inputs tot he card, then convert them to usable numbers for my project.
I havent actually finished it yet, but I really dont see the problem with getting the programming out of the way early in the project as long as you write in a powerful enough language so that it can do the things you need it to, rather than using Q-Basic or something I'm using Visual Basic on mine, which has some pretty powerful controls for interfacing, but C++ would probably be the most ideal for the actual gateway between the card and your program.

[stimps]

I feel sad. I didnt understand any of that:( what is the launguage that mplabs ide use to write the program in the PIC?

[Richard OConnell]

Sorry stimps,
I didn't mean to confuse you. I'm not sure what language the PIC is programmed in. I'm taking a slightly different approach and I want the hardware or PIC board to serve only as a gateway or a way to "pipe" the information to a computer in a way that is more useful to me. That would most likely minimize the amout of programming needed on the PIC/PLC and allow me to keep most of the important functions and equations organized in the executable program itself. I apologise if I am still confusing you and really, I might be looking at this whole thing wrong and only confusing myself in the process. A friend of mine has been working with PICs/PLCs for 30 years and he ssaid he would give me a hand if I needed it, so I might take him up on it.

[stimps]

Thats cool, yeh i went back later to this post and forgotten later that you were using a pc as well as a PIC . Well i really am hell bent on making my own pic based ecu, but having never done pic stuff before, am just really struggling with it. I have the pic kit2 and have been trying to make sense of it all but not alot is really sinking in. The one i have i think uses C. I need to figure out how to set up a pwm system and enter variables, drive a display, etc. Rather over my head. I do have a plc i can use but that will make it rather limited.

[g8rpi]

Hi Stimps,
Sory for the slow response, I've been in Ghana West Africa.
I think you may ave mis-typed the PIC part number. Microchip don't list a 16F626. The 16F627 is not ideal as it does not have an analoge to digital converter module( ADC). The cost of the chips is so low that for small quantity applications it's not worth trying to skimp on performance. You want a chip with ADC, Hardware PWM and a UART (or USART). I used a 16F877A. Microchip suggest the newer 16F887 as an alternative. Ithe '887 has an internal oscillator option so you don't have to use an crystal (but can if you wish). The 40 pin chip insures that you don't have to compromise on which features you can use. It also means you don't have to do things like multiplexing the dispaly and control buttons. It's OK to save a few cents on a smaller chip when building 1000's of units, but better for us to spend $5 more on a chip and simplify the software.

Regards,
Robert G8RPI.

[stimps]

Yeah thats the one, possible typo. Is that the same as the pickit2 one? Should i just order a new chip and use a prototype board?

[stimps]

Hey G8rpi, i like this, If i was to try this, what inputs/outputs pins are you using with this, and will it work with a Pic16F887? I think thats the one with the extra pins and features, but basically similar to yours?

Also, which program do I used to program that code into the chip? reason I ask is it doesnt look like the C code im used to seeing when i used my software that came with my PICKIT2, ie, the MPlabs IDE.

cheers, and thanks for sharing your code:)

Nov 5, 2010 17:07:43 GMT -5 g8rpi said:

Hi Stimps,
Here is some code I wrote to read a standard tachogenerator and display % RPM on an LCD.

'25 Dec 2002
'Robert Atkinson
'Test software for pulsin to read GT tacho, 70Hz = 100%
'PBP 2.41, PIC16F84 4Mhz


'DEFINES------------------------------------------

DEFINE LCD_RSREG PORTB 'USE PORT B FOR RS SIGNAL TO LCD
DEFINE LCD_RSBIT 7 'USE b7 TO KEEP REST OF PORT CLEAR FOR MUX
DEFINE LCD_EREG PORTA 'USE PORT A FOR ENABLE lcd TO STOP MUX CAUSING PROBLEMS
DEFINE LCD_EBIT 4 'USE a4 FOR ENABLE

DEFINE PULSIN_MAX 41000 ' LIMIT MAXIMUM COUNT TIME TO 0.41S

'PORT ALLOCATIONS---------------------------------


IPP var PORTB.0 'INPUT PULSE FROM TACHO

'VARIABLES-----------------------------------------
RPM VAR WORD 'PERCENT RPM BASED ON 1/2 WAVE RECTIFICATION

PW VAR WORD 'ACTUAL PULSE WIDTH

'INITALISE PORTS-------------------------------------------------
PW = 0
RPM = 0

PAUSE 1000 'ALLOW LCD TO INIALISE


MAIN:

LCDOUT $FE,1, "RPM TEST V1.0" 'POWER UP CONFIDENCE CHECK
PAUSE 800 'TIME TO SEE LCD

lOOP:

PULSIN IPP, 1, PW

RPM = 35700 / (PW / 2) 'CALCULATION OF PERCENT BASED ON 2 POLE 4200 RPM = 100%
'35700 USED DUE TO 16 BIT MATH LIMIT
IF PW <400 OR PW >40000 THEN 'TRAP UNDER AND OVER PULSE WIDTHS
RPM = 0
ENDIF

LCDOUT $FE,1, "PULSE WIDTH ", #PW 'DISPLAY PULSE WIDTH 10uS RESOLUTION
LCDOUT $FE,$C0, "% RPM ", #RPM 'DISPLAY % RPM


PAUSE 200 'PAUSE TO SEE LCD
GOTO LOOP

END

Nothig great but it works ;-)

[saiello2061]

Hi All,
I've been attempting to build a full blown datalogger/display/control system too. My way:

PC/laptop <-> VB6 software <-> usb <-> Arduino/Seeeduino M/C <-> sensors/actuators

I have developed a Gauge control in VB that allows the programmer to fully define the needle style and behaviour as well as have a background bitmap for the gauge picture. Attachment shows early testing/development showing just a few very basic examples of the styles that can be generated from the single control. Shadowed 3D affects can be had with the right parameters. I have also gone some way to develop 3D graphical controls for switches, LEDS and digital panel meter displays.
The M/C in this system simply acts as a go-between. It accepts instructions from the VB software to read/write inputs/outputs. The M/C then reads/writes to the correct sensor via the ADC's/DAC's.
You can use the M/C's native analogue inputs/outputs although they are limited in number and usually only to 10bit resolution. I have an addon board that allows expansion on the number of input/ouput ports with 12bit resolution using additional ADC's and DAC's.
The usb conection is actually used to simulate serial comms, so in VB you only need to know how to use the MSCOMM control to be able to talk to the microcontroller. In fact it is this serial connection that is also used to program the M/C via an IDE on the PC using C/C++. Having heard about PIC's M/C's and various others, I then stumbled upon the Arduino and when I read how easy it was to set up an Arduino and the development environment on a PC, I almost thought it was a joke... ;o)

This is on the back burner at the moment, I'm in the process of building relatively small boxed standalone M/C system using graphical LCD for monitoring rpm, temp and pressure with various analogue/graph type display options, user defined alarm setpoints triggering a relay and limited datalogging facility for playback.

Attachments:

[ernie wrenn]

Check out this iterface board on E-bay: 180537743599


16 channel serial port. Looks interesting.

Look at their other boards and drivers..

Ernie

[turborico]

Interesting discussion!

I'm a complete n00b in the DIY gas turbines, but I've been throwing around the idea of using a microprocessor to monitor the engine, and maybe if I learn enough, to control it almost entirely.

I apologize if they have been discussed before, but the Arduino boards seem to fit the bill pretty nicely. They are cheap (~$25 US), programmable over USB, and with a language similar to C++, and it seems like it's very flexible as far as digital & analogue I/O goes. Plus, it's open-source, so there's a ton of support for it.

I've got a long road ahead of me, I haven't had much luck in finding any information on the subject so far, and I don't know squat about programming...

[ernie wrenn]

Turborico

You have come to the right board. In the short time the board has been up, The discussions have been mind bending. I have learned more math in the last few weeks than I did throughout school and still failed the test.

I you have any questions or need info... ask! This board is here for your safety and brain trust.

Thanks for your service..

Ernie