Sinking current - How to pull down a point to zero using Arduino pins

attaching the images.

Take a look at this post.

The two leads that say "To Arduino" originally went into the integrated circuit,

The chip might be a receiver chip, which means it is not necessary for your application and should be removed as it was in the other post. Trace the connections from the chip to the power transistors.

Well, the pictures made things immediately clear, didn't they?

Could have saved a lot of time!

I've looked at your voltage divider.
First, I have to assume the IC pin is some type of input?
What kind of input is it.
Does it source, sink or hi-impedance?

If it sources, the divider is not likely to pull it down
to 0V when D5 is 0 because there will be some drop
across the top resistor. If it is a source, it will be
loaded down by the divider so that it may not reach
a high enough level to work.

If it is a sink, the resistor will limit the current to it as well
as reduce the voltage from the output D5. D5 may not
pull it high enough to be considered a high input.

If it is hi-impedance, it will at most slow the signal down
and may still not raise the level of voltage high enough
for the IC input.

Since you can't find a data sheet, I have to assume it is
an in house number. I suspect it is a driver chip for the
H bridge transistors.
A back trace of the controlling wires might help to
understand how these might expect to be driven.
I suspect there is a transistor and resistor connected
to each and what rails these two are connected too.
Dwight

It's an RC car. The chip is the radio receiver TAIYA 3-R. Since the receiver is being bypassed for the project it is unnecessary and can be removed. The H-bridge (the heatsinked power transistors) are normally driven by the Receiver chip via resistors. At this point , we have no further information until the OP traces the pins from the chip to the base resistors and then to the power transistor base pins. This can be done more easily by looking at the number on the power transistor, finding the datasheet and finding out which pin is the base pin and then tracing it backwards from there back to the chip which will tell you which pins on the chip are outputs. If it is indeed a receiver chip, there are no "input" pins per se because the input is the radio signal coming in on the antenna, which is decoded by the chip to FORWARD, LEFT,RIGHT and REVERSE. The steering would be independent of the forward and reverse, unless it uses differential drive. We don't know what the car frame looks like so that's an unknown. We need a picture of the bottom of the car.

raschemmel:
It's an RC car. The chip is the radio receiver TAIYA 3-R. Since the receiver is being bypassed for the project it is unnecessary and can be removed. The H-bridge (the heatsinked power transistors) are normally driven by the Receiver chip via resistors. At this point , we have no further information until the OP traces the pins from the chip to the base resistors and then to the power transistor base pins. This can be done more easily by looking at the number on the power transistor, finding the datasheet and finding out which pin is the base pin and then tracing it backwards from there back to the chip which will tell you which pins on the chip are outputs. If it is indeed a receiver chip, there are no "input" pins per se because the input is the radio signal coming in on the antenna, which is decoded by the chip to FORWARD, LEFT,RIGHT and REVERSE. The steering would be independent of the forward and reverse, unless it uses differential drive. We don't know what the car frame looks like so that's an unknown. We need a picture of the bottom of the car.

Agreed
Dwight

@raschemmel
"one side motors working" does not a working RC car make.
Sir, Both sides of the car / both motors are working . They are controlled by 4 lines.

What about this ?

@raschemmel
I do not know what signals are there from those control points. I just measured voltage between the point and the ground. Also measured the current when directly sinking to the ground. (When directly sinking one point to the ground I got one side motors working.) I do not have a scope to check the signals.
By "academic" , I do not have a real project in hand ? No.. I have some thing solid before me.
Or did you mean .. that discussion is going too theoretical ? .. sorry I cant help :wink: asking questions.

Where's the TRUTH TABLE that shows what function is controlled by what pin/point and what voltage is
on the pin when it is not being jumpered to Ground ?

You tell us you have it working but nothing about what controls what or how you make it do this or that. You need to start by being more organized. Stop referring to the four controls lines in general and identify them specifically. Give each one a name that describes what it does. If you cannot associate a specific function with a speciific pin then name them A,B,C & D and post a truth table showing what conditions on the four control lines result in what actions. We still don't know anything about that. In one post you say you got one side working but no mention about the other side. There has been no mention of steering and now you tell us both sides are working but we still don't have a TRUTH TABLE. You have a meter. Why don't you look at the numbers on the heat sinked devices and post those and look for the datasheets. Tell what all the functions are and how they operate.(exactly), not in general (ie:" grounding some points makes the motors work ...." is no help at all)
Be specific.
What do you propose to do with a receiver chip if you are not going to use it ? Are you planning to leave it in the board ?

Of interest is how much current was involved with shorting places in the circuit
to ground?
Dwight

dwightthinker:
Of interest is how much current was involved with shorting places in the circuit
to ground?
Dwight

As already mentioned less than 5mA. Mostly 1mA.

raschemmel:
....both sides are working but we still don't have a TRUTH TABLE. You have a meter. Why don't you look at the numbers on the heat sinked devices and post those and look for the datasheets. Tell what all the functions are and how they operate.(exactly), not in general (ie:" grounding some points makes the motors work ...." is no help at all)
Be specific.
What do you propose to do with a receiver chip if you are not going to use it ? Are you planning to leave it in the board ?

I could not find time make the truth table. I did not try all combinations.
Here is what I tried today:
Connected so called control lines to arduino digital pins through transistors ( open collector ).
I was trying to make the RC work through bluetooth app in the android phone.

It worked good for the forward function ie; both side motors worked in the same direction as expected
as response to my forward button press in the android app. ( by the way , it is a differential drive RC car)

I do not plan to use the TAIYO IC on the board. But neither I do not plan to remove it. I think it is NOT going to harm anyway.

Post pic and video only show what car it is.

Youtube link

I am met with a set back on this interesting project a few hours back. :frowning:
Changed the battery to a new 12 V one ( when the 6V got drained) , without considering the
bluetooth module.

It just got fried. I think only the voltage regulator on the HC-05 board got burnt. ( but not sure if I can
just do some work around)
That was my only BT module and I need to order new one.

So sad .. to lose the flow .. and impatient to get this working. :frowning: :frowning:

I don't have to tell you how dumb that sounds, even for a noobie.
What were you thinking?
WHY were you powering the BT module from 6V instead of from arduino 5V with the 6V battery connected to VIN of arduino ?
Here on the forum , we don't whiite wash things. We don't call that a "set back".
We call that a "fxckup". (I think the British call it a "Stuffup". (you "stuffed it"). A "setback" is ordering PNP transistors instead of NPN. when there's a 2-week lead time.
Here today, gone tomorrow.
Why didn't you recharge 6V battery ?
All RC cars have rechargable batteries.
Still need truth table.
You did all this JUST to control it from your phone?

You have the freedom to call it whatever you want until it becomes a nuisance. Hopefully people will be considerate for the highly experienced.

Agree.. I was dumb to connect the Bluetooth module directly from Vcc.

I want to use mobile phone for many other sensors and controls , like GPS , accelerometer etc. This will save me from busy separate sensors for each and wiring them, and programming them.

raschemmel:
You did all this JUST to control it from your phone?

raschemmel ,I am curious , you did have some great ideas in mind , when seeing my original post? (I can try them too.)

I still can try the OTG connection instead of Bluetooth.

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

OTG ?

On The Go

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.

dwightthinker:
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.

dwightthinker:
..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 )

raschemmel:
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.