Go Down

Topic: Digital Transistor? (Read 604 times) previous topic - next topic

cyclegadget


I am wanting to simulate a rotary switch circuit that has 6 different resistors on it. As the switch rotates a different resistor is selected letting an engine ECU know what gear a motorcycle engine is in.

I need a way to simulate the switch with changing resistance. It will be a series circuit, with current being the variable.

Is there a chip or device that could be ran with I2C or SPI that could do this task. If a transistor is the only choice I will make that work.

Any suggestions are welcome.
Thanks,
Mark
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

retrolefty

Yes, there are I2C and SPI 'programmable pot' chips avalible that allow one to set it's input to output resistance via software. You will have to see if the voltage input and maximum current limits are compatible with your application however.

Lefty

Grumpy_Mike

Quote
As the switch rotates a different resistor is selected letting an engine ECU know what gear a motorcycle engine is in.

That sounds like heavy current, not the sort of thing you can get a chip to do.
Have you measured the current or do you know the resistor values and voltage?

cyclegadget

Thanks with the replies so far.

The voltage range would be "open" 0 volts to a maximum of 5 volts from the supply.

I know that one resistor is 6.8k ohm, I am looking into what the rest of them are. I will get back to thread with that info. I am sure it is low current as this circuit is just for signals and not relays.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

DVDdoug

Quote
am wanting to simulate a rotary switch circuit that has 6 different resistors on it. As the switch rotates a different resistor is selected letting an engine ECU know what gear a motorcycle engine is in....

...with current being the variable.
Six transistors connected to 6 different resistors should work.

Quote
That sounds like heavy current, not the sort of thing you can get a chip to do.
Maybe not...  If I understand correctly, he is only (simulating) sensing which gear is selected, he's not actually moving a gear lever.

Quote
Have you measured the current or do you know the resistor values and voltage?
Right... He has to know what value & wattage resistors to use.

cyclegadget


Here are the resistors, and calculated current I would have to simulate with a supply of 5 volts.

1.Gear  0.6 Kohm  = 8.3ma

2.Gear 0.9 Kohm   = 5.5ma

3.Gear 1.6 Kohm   = 3.1ma

4.Gear 3.0 Kohm   =  1.67ma

5.Gear 7.5 Kohm   = .67ma

6.Gear  16. Kohm
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

MarkT

A schematic of how this switch connects to the 12V supply and ECU would be useful...
[ I won't respond to messages, use the forum please ]

cyclegadget


   GND (-)............selected resistor.....ECU with 5volt sensor power.

  I don't know what circuit is in the ecu. I may have to take a measurement with a resistor in place.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

dc42

As the resistors are connected to ground, I would consider using 5 or 6 2N7000 small signal mosfets driven from digital pins. Bipolar transistors might work, but the saturation voltage of a bipolar transistor voltage might cause problems, depending on how the ECU senses the resistance.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

liudr


As the resistors are connected to ground, I would consider using 5 or 6 2N7000 small signal mosfets driven from digital pins. Bipolar transistors might work, but the saturation voltage of a bipolar transistor voltage might cause problems, depending on how the ECU senses the resistance.


GND to transistor source pin, arduino pin to transistor gate pin, resistor one side to transistor drain pin. Then five resistors other side all connected together and to ECU. It's nice to learn something (motorcycles use resistors to indicate gears) right at quitting time.

cyclegadget


Thanks for the replies. So far I have the pins available to use the transistors so that is definitely and option.

I hope to do more testing tomorrow.

Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

Go Up