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Topic: Sinking current - How to pull down a point to zero using Arduino pins (Read 4261 times) previous topic - next topic

dwightthinker

I do hope you see why the voltage divider won't work.
If the pin is intended to be pulled to 0 volts, you may
not get that close.
With 1ma source, 2K will be at 2V at the top. This may
be enough to partially turn on the transistor to the
motor, when it should be off.
When the Arduino pulls down, there well be 1V at the
top of the divider. Again, that may not be enough to
properly turn on the drive, causing more power loss
in the drive transistor.
Not knowing the circuit of the drive the divider is clearly
a bad idea.
Now, you connect 12V. Again, not knowing the circuit
attached, the 2:1 divider could be putting 6V on the
Arduino.
Dwight

raschemmel

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

raschemmel

Quote
Agree.. I was dumb to connect the Bluetooth module directly from Vcc.  
I don't know WHICH Vcc you are referring to.
Technically, when discussing ANY (5V) arduino, Vcc is 5Vdc

What I meant was that your battery (regardless of the voltage as long as it is <12V) should be connected to "VIN" of the arduino (the input for the onboard 5V regulator).
ANY device that runs on 5V (like the BT) should be connected to Vcc (5V).
Had that been the case , the 12V battery would have provided 12V to the onboard arduino regulator , which would then have provided 5V to Vcc , and thus to the BT, and there would have been NO problem.

I have no idea what you are talking about. Please post a schematic of how your BT ,battery, and arduino are connected . (photo of hand drawn schematic )(please don't use Fritzing)

Since the control lines come from the IC, which I am fairly certain is the RF receiver, they are probably open collector outputs that are used to drive ACTIVE LOW motor power transistors. I have no idea if they are NPN or PNP but the OP says the motor turns on when those control lines are grounded , suggesting PNP transistors on the heat sinks. I have repeatedly asked the OP to look at the numbers on the power transistors but my requests have fallen on deaf ears.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Ajan

I do hope you see why the voltage divider won't work.
........
With 1ma source, 2K will be at 2V at the top. This may
be enough to partially turn on the transistor to the
motor, when it should be off.
When the Arduino pulls down, there well be 1V at the
top of the divider. Again, that may not be enough to
properly turn on the drive, causing more power loss
in the drive transistor.
........
Thank you for the reply. I have thought about two questions while considering he VD( voltage divider):

1. If the current through R1 to the ground through arduino sink pin is enough to properly ground the so called control point
2. If the R1+R2  good enough to prevent grounding of the same point
I already had tried some R1 and R2 values and found one to be working good. ie; R1 will short it while R+R2 will still keep it high. The diagram is representative , the R values are not exact.

..Now, you connect 12V. Again, not knowing the circuit
attached, the 2:1 divider could be putting 6V on the
Arduino.
Dwight
I was onnecting 12V to Vin or arduino  and used the same tie point in the bread board to connect the BT module.
I did this by mistake ( accidentally / forgot to change the power to 5V point) . I DID know that it will fry the module. 

I agree .. this will cause 6V to my arduino pin -- if I use the Voltage divider. But did not use it and as per the suggestions and discussions I have dropped the idea of using VD and used transistors to control.
( Open collector )

Ajan

I don't know WHICH Vcc you are referring to.
...
What I meant was that your battery (regardless of the voltage as long as it is <12V) should be connected to "VIN" of the arduino (the input for the onboard 5V regulator)..
.....
I have no idea if they are NPN or PNP but the OP says the motor turns on when those control lines are grounded , suggesting PNP transistors on the heat sinks. I have repeatedly asked the OP to look at the numbers on the power transistors but my requests have fallen on deaf ears.
I connected it to Vin .  I should have connected the BT module to 5V out from Arduiono.
Yet to disassemble the heat sinks and check the driver transistor types.  Will keep you posted.


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