Arduino controlled wheelchair

[gcebiker]

...well somethings not quite right, powered the emulator up to the chair and all was well...

Till i pressed the software on button...magic white smoke from the MAX485 chip

I only have it powered via the Arduino, or so i thought...well back to the drawing board

[gcebiker]

...well somethings not quite right, powered the emulator up to the chair and all was well...

Till i pressed the software on button...magic white smoke from the MAX485 chip

I only have it powered via the Arduino, or so i thought...well back to the drawing board

Turns out the whole board is fried... i will build the new board with a switch mode Vreg instead of the LM7812 or maybe use the LM7812 to provide the pulse voltage and a switch mode to power the emulator.

DG419 needs current limiting too.

[gcebiker]

I am such a dummy, the DG419 spec sheet says

Digital Inputs VS, VD (Note 1) .........(V- - 2V) to (V+ + 2V) or 30mA
(whichever occurs first)
Continuous Current (any terminal) (Note 1) ........................30mA
Peak Current, S or D (pulsed at 1ms, 10% duty cycle max)..100mA

So i need a resistor from the Arduino Digital pin to the signal pin of the DG419...and a 1.2k 1.5watt resistor on the 12+ 'pulse' pin.

Maybe the board is ok and i just fried the DG419 by loading it with full battery current/voltage
...everything on the board however...is cooked inc another RS485 module(because i plugged a new one in with out replacing the DG419 first ).

Thankfully i have about 55 of them left in the shed... thanks to an ordering mistake on my part.

[gcebiker]

Replaced
- Arduino Nano V3.0
- DG419 analog switch
- Max485 breakout board

Added
- 1k 1W power resistor to S2 of the DG419 (on pulse pin)
- Thumb joystick wiring (and left the Wii Nunchuck wiring) - so i can flip between versions of code for comparison.

The LM7812 gets REAL warm...and only took about 10minutes, just ordered some of the regulators Woody uses in his BT JC2000 remote.

The 5V 5w version - http://au.element14.com/tracopower/tsr- ... dp/1696320
and the 12v 12w version - http://au.element14.com/tracopower/tsr- ... dp/1672130

By accident i noticed when switching from 15v plug pack (that charges the 16v filter cap connected to the LM7812), there is enough juice in it to get the base to respond to an on pulse even at 5v (due to residual charge in the Capacitor)

Maybe i could do a charge pump to get the 16v cap charged from 5v but i was hoping for a nice simple board anyone could copy and populate (as i have just stuck to plug in modules)

[Burgerman]

Its all beyond me anyway, but KISS would apply!

[gcebiker]

Testing

Before making up a new board - i did some checks.
- LM7812 as regulator.
- Pulse 'on' voltage taken from output of 7812 via 1k 1watt resistor.

Results - emulator powered from
5v USB - no response from base (no big surprise there)
15v plug pack - no response from base - output of 7812 is 12v (more than 12v needed for base to respond)
24v XLR ie full battery volts - no response from base - output of 7812 is 12v (more than 12v needed for base to respond)

Rewired 1K 1w resistor to Vin of emulator.
Pulse 'on' voltage taken from INPUT of 7812 via 1k 1watt resistor.
15v plug pack - no response
24v XLR - base responded for a short time before the LM7812 Vreg shat itself and took out the rest of the components....

This is has turned into a very expensive habit.

But on the up side, base responded so i know i can use the 5V 5w version of the regulator (which was the point of doing the tests anyway)
http://au.element14.com/tracopower/tsr- ... dp/1696320

I am just hoping there is enough juice to run the emulator and the Wii , if not i have 5 of each coming and i can just put two on the dev board.

I have just realized i might get lucky and the DG419 may have survived...its rated for 30v

[gcebiker]

Post Mortem
Luck must be on my side, i only fried the Arduino and the LM7812.

I started off with the Max 485 in the breakout boards as i did not know what i was doing..and i still have little idea but going to try a build with the basic chip and PnP, NpN back to back to make the pulse 'on' switch.



Cheaper , fewer components, easier to wire up and i wont need a 12v supply for the DG419 (tho i could just run them straight from the 24v lines)

Data Capture

[gcebiker]

First go with Fritzing - trying to draw up a shield for Arduino Nano V3.0 - Shark Wheelchair controller emulator.

The pins pretty well match up with the drawing.

Will move over to software serial.
- 7805 represents the Tracopower 24v - 5v regulator.
Resistor values are
- 22k for output of Max485
- 1k 1W between 24v in and NpN transistor.

Tho hard to see the Base of both transistors are joined and connect to D6, to make a break before make switch.

The bread board is not quite to scale, i had to make it wider to fit the components on the drawing and make the wires clearer.
The outside row is left bank to fit headers for a joystick or Wii

Not sure where the dotted line came from...and cant figure out how to remove it yet.

[gcebiker]

Figured out the pic, will post code after i built/test it.


I may have the A/B outputs of the Max485 back to front, the inverted one needs to go to the PnP/NpN switch but i hope you all get the idea a bit clearer.

sooo wishing i had known what i was doing to start with, this is much simpler than my test rig but i could not have gotten here with out it and the help of Irving.

To that end, Irving if this works and you are interested.
I would like to build you one and send it over, if you would maybe have a use for it.
- A complete emulator (after i test it a lot more and work out the code).

After i get the bugs on this sorted out i plan on an inline module, so the factory joy stays in place and the Speed/Direction values are modified depending on the sensor data.

AND after i get the Dynamic Shark worked out...time to open up the Qlogic controller in the shed

[gcebiker]

Built and tested Arduino nano V3.0 Shield Shark Remote emulator.






- Base not yet responding, output looks correct
- likely that the 1k 1W resistor is to big (base requires 40mA pulse)

I am using a BC337 NpN as the pulse on switch so i can go right up to 800mA
- will try other resistor values tomorrow.

Using generic PnP for data transistor, PN200 and BC556.



I still have to get the code sorted out but this (the attached code) works with the shield below, output is correct as per Logic Capture.
- its a work in progress.
- now uses software serial (previously hardware UART)

[gcebiker]

Emulator is ...kinda working, logic capture looks ok...but no response from base.
I took out the 1k Power resistor and put in a 470ohm, its got to be something like i have a transistor in backwards...

I am thinking i have the Transistors wired wrong (on the board it self)

Does this schematic look ok ? anyone got any ideas ?

And whats the best way to get from Schematic to making some boards up ?

[Irving]

Its hard to read that circuit, I've lost track of what its trying to do. What are the pins on the Arduino and J1. The transistor connection arrangement looks odd... Its not obvious where the 24v connection and ground go...

[gcebiker]

In the sketch,

Arduino pin D6 (the pink wire) goes high, switching off the PnP transistor Q1 and turning on the NpN transistor Q2.

This lets 24v pass via the 470ohm resistor, thru Q2 and out via J2 (Shark Bus High)

after 300ms D6 goes low, turning off the NpN (and thus the 24v 'on' pulse), turning on the PnP Q1 and connecting the data from 'A' of the Max485 to 'Shark Bus High'

'B' of the Max485 is directly connected to J2 and 'Shark Bus Low'

Q1 the PnP, is to be on when D6 is low...which is all of the time , except for when Shark Joystick Emulator is turned on
Q2 the NpN is only on for the 300ms 24v pulse needed to latch the Shark Power Module 'on'

I was using the DG419 for this purpose previously.

The Transistors have the wrong pin numbering, i am reading up on how to modify the parts at the moment to correct the incorrect pin numbering.

Eventually this will go inline, the 4 core cable between the Joystick and the Power base providing the power in and the J2 data out.
For now i am jacked into the XLR with a 3.5mm plug/socket to provide power / ground, and i have tapped the shark bus to inject the signal.

Code: Select all

void sharkStartup () {

  digitalWrite(dePin, HIGH); // Hold dePin high when transmitting.
  digitalWrite(rePin, HIGH); //
  {
    digitalWrite(dataSwitch, HIGH);    // Flip data switch, HIGH = PNP 'Off', NPN 'ON'
    delay(298);
    digitalWrite(dataSwitch, LOW);    // Flip dats switch, LOW = PNP 'On', NPN 'Off'
    delay(10);
  }

  {
    /*build start up packet
       I've yet to put the factory notes in here but it will change for each emulator as its just
       the date of manufacture and such boring stuff...
    */

    data[0] = (0x74);   //
    data[1] = (130);    //
    data[2] = (133);    //
    data[3] = (130);    //
    data[4] = (128);    //
    data[5] = (136);    //
    data[6] = (205);    //
    data[7] = (160);    //
    data[8] = (128);    //
    byte sum = 0;
    for (int i = 0; i < 9; i++)
      sum += data[i] & 0x7f;
    data[9] = 0x7f - sum;       //Checksum  OK = (141)
    data[10] = (15);      // all packets end with this identifier

    for (unsigned char i = 0; i < 11; i++)
      sharkSerial.write(data[i]);
  }
  digitalWrite(dePin, LOW); // Low to enable RX on max485
  digitalWrite(rePin, LOW); //
}


[gcebiker]

Well i feel like a dummy.

I was reading the schematic diagrams as tho they were top down, turns out some are some are not.
In my case both were looking at the bottom of the Transistor, which means i have put both Q1 and Q2 in back to front ..

I knew it had to be something simple.
Found the wiring issue by making it up again on a soft wired prototype board.

[gcebiker]

I was wrong again...not surprising really, i am so fried today.

Q1 is wired back to front, and not shown on the schematic is a 10k resistor i put between the Arduino D6 and the Base...

Taking the resistor out gets the Arduino led blink program, to do the correct 'train crossing lights' type blinking,

Q2 is ok and the schematic is ok ...i think, i just have not wired it physically how the schematic does (i did the schematic after i did it physically)

[gcebiker]

..still going in circles.

I had it working months ago, or so i thought but today, cant get it to work.
Maybe i never had it working and so went over to the DG419's , had to be some reason i purchased $100 bucks worth of chips

Joining the outputs just gets me gibberish.

[gcebiker]

I found it helps to have the bread board pins in the right holes.

So after a day going in circles , i think Q1 is wired backwards on the physical board, schematic ok ?

I know i could just use to of the Digital pins to operate the transistors independently and i ended up trying that earlier tonight but it was bugging me why could i not get the single digital pin to work both transistors...well with a brighter torch i could see i had the base connected to the wrong digital pin

[Irving]

I'm not convinced this circuit will work. Consider Q2 - this will only turn on if its base is 0.7v above the emitter potential. In other words the emitter is always 0.7v below the base voltage. Since this is driven by the Arduino @ 5v the 'pulse' to the Shark controller will never be more than 4.3v. I understood you needed a higher voltage than this.

The diagram below shows the result of simulating this circuit. Resistors R5, R6, R8, R9 and capacitors C1 - C4 model the input resistance & capacitance of the MAX485 receiver at each end of the line. The data stream is random but included to show how Q1's base-emitter clamping reduces the differential RS485 voltage on one side - preventing it falling below ~1v. There is a lot of noise caused by Q2 conducting slightly on the trailing edge of the signal due to line and device capacitances. This might affect the integrity of the 485 receiver in the controller and could be why its not responding.

[Irving]

here's a better simulation using a proper line transceiver. Note the second pulse generator to inhibit the transmitter before sending the pulse, still limited to 4.3v though.

Basically, to get to the required 12v pulse we need a level shifter. Here's two approaches, the first uses an optocoupler and the second a npn-pnp pair. Both also use a 12v zener diode to set the voltage. The optocoupler has the advantage of simplicity but potentially a couple of $ more.

[gcebiker]

I'm not convinced this circuit will work. Consider Q2 - this will only turn on if its base is 0.7v above the emitter potential. In other words the emitter is always 0.7v below the base voltage. Since this is driven by the Arduino @ 5v the 'pulse' to the Shark controller will never be more than 4.3v. I understood you needed a higher voltage than this.

At first i did not understand (when reading the above).
Then i fixed my board tested it and it did not work (no response from base despite apparent correct signal)

Back tracking to other things i did a few weeks ago with Arduino / NpN mosfet i was turning on a 12v fan using PWM from a 28v supply.
The difference i could see was i was connecting the low side of the circuit.

In this application i am connecting high side and the transistor, though conducting , its not turning fully on ? so i am not getting a "higher than 12v pulse"....only a Logic level pulse (which i see on the Logic Analyzer)...and again wishing i had a digital scope, as i would have seen it right away.

The SBH wire is also used by the SR to "wake up" the SPM by asserting more than 12V (actually, it asserts full battery voltage
less about a volt) on SBH. The driver for this function in the SR is required to drive the 270 ohm resistors at the SR and SPM
ends.

Notes about the terminators:
- In theory, the 270 ohm terminator at the SPM end will be disabled (as it is when the SPM is powered down) but there are other
circumstances where the terminator will be turned on.
- The terminator enabling transistor in the SPM may be turned on unpredictably during the power-up period.
- The SR shall disable its own terminator when asserting the wakeup signal.

The wakeup signal on the SBH wire shall be asserted for 300ms +/- 20ms. During this time, the SPM is required to power up,
stabilise its operation and latch its power on so that it does not power down again when the wakeup signal is removed.

Note that communication on the Shark Bus is not possible when wakeup signal is present.

The wakeup signal transmitter shall be designed so that it can source 40mA at greater than 12V, under all normal battery conditions (see Hardware Specification), for the full 300ms.

Seems like i have to go back to using the DG419 cmos switch.
or go over to an Opto as you suggest.

[gcebiker]

I am confused,

The way i am using the BC337 NpN transistor:
- 24v is at the Collector
- Emitter is connected to Shark Bus High (where 0v is 'off' ).

So the Vbe should be ok with it fully on at 5v high from the Arduino ?
Base is supposed to turn on at 1.2v (emitter voltage is 0v)

Is this use of an NpN considered a Capacitance switch, ie its not driving a load ? and is it that which changes the need for higher Base Voltage ?

H-Bridges driving motors drive higher load voltages from logic level inputs, so i thought this would work...it works on the bread board with only 5V going to the NpN.

[gcebiker]

Incidentally ..

Discharging a 16v 470uf Electrolytic is also enough to latch the power base on.

Found that out by accident a few days ago.

I have the DG419 cmos switches here, they work, the base responds...
I have started to build a new board, no point in mucking about any longer, if i have the stuff here and i know it works

[Irving]

I am confused,

The way i am using the BC337 NpN transistor:
- 24v is at the Collector
- Emitter is connected to Shark Bus High (where 0v is 'off' ).

So the Vbe should be ok with it fully on at 5v high from the Arduino ?
Base is supposed to turn on at 1.2v (emitter voltage is 0v)

Is this use of an NpN considered a Capacitance switch, ie its not driving a load ? and is it that which changes the need for higher Base Voltage ?

H-Bridges driving motors drive higher load voltages from logic level inputs, so i thought this would work...it works on the bread board with only 5V going to the NpN.

You've a little to learn about BJT. The base to emitter differential, nominally 0.7v but could be higher eg 1.2v is a fixed value. If the base is at v1 volts the emitter is at least v1 - Vbe to allow the transistor to turn on. If in doing so the emitter voltage rises the transistor will turn off until a steady state is reached where the collector-emitter current through the load to ground gives an emitter voltage of v1-Vbe. This configuration is called an emitter follower and is an example of a constant current drive. However, something I didn't pick up on is the 40mA requirement. This is to force the bus high even when someone is sending - you need to override the low impedance of the bus driver - and an emitter follower won't do.

To meet the 40mA requirement I've modelled a couple of alternate solutions, below, using a PNP transistor or a P-channel FET. I've also added a diode which maintains better isolation from the bus.

Post the schematic how you are using the DG419...

[gcebiker]

Video of builds, sound is a bit low so you may need to turn your speakers up a bit.
...the motors are moving but its pretty hard to hear them, you can just make out the sound of brakes latching and releasing.

Its a work in progress. https://www.youtube.com/watch?v=YVvPwSw ... e=youtu.be

[gcebiker]

Post the schematic how you are using the DG419...

Ive not got one yet, i will as soon as i draw it up.

[gcebiker]

This is the best i have on hand at the moment, the schematic looks a bit weird...

I have put some notes on the picture to try and clear up any questions you might have Irving.



...what i dont have pictured there (it gets very crowded) , the signal diodes and small cap on the V+ / Gnd lines.
as per notes, V+ is not drawn in either but it goes to the 1K resistor output, which is the thicker green wire in the video.

[gcebiker]

Same but colour coded.

I'll try to get this made up over the next few days.

[gcebiker]

// mistake in that drawing above, tiny Yellow wire at the top of the DG419 should go to ground.

Pic with pinouts from datasheet.
- not sure pin 6 needs the 10k resistor...I've not put one in and its working for now...
- pin 4 takes 10v - 30v so its just wired straight to the battery,
- Maxim DG419 !!! other branded chips do not operate at full battery voltage.

[gcebiker]

Fixed up wiring mistakes, wired up half of the board today before brain gave way, small steps.

I may have to swap out the 470ohm 1W resistor i am actually using for the 1k 1watt that's in the prototype board

!! NOTE - for anyone reading this post without having read the thread
- BOARD NOT TO SCALE !! don't literally use the pin spacing in the picture if you are using an Arduino Nano V3.0

[Burgerman]

Your voltage reg chip legs are bent.