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Topic: Sinking current - How to pull down a point to zero using Arduino pins (Read 4112 times) previous topic - next topic

raschemmel

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

Ajan

@Paulcet

Thanks for the suggestions and your precious time to suggest courses on electronics.
( as answer to my question on why voltage divider is not a good idea in this context )


How would I know what is in his mind? :smiley-eek:
Without the pictures we have requested (haven't we?  Can't imagine why not!), we don't quite know
I have already posted a diagram which shows the IC control pin being grounded through a voltage divider.
Also mentioned about the feable current in the control lines.

@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.


People here are really trying to help me getting the RC work, more than teaching the answer to the
question on the voltage divider. :-) Thank you all.

I am attaching pictures of the control board. TAIYO 93-R in the IC used- sadly I was not able to find a data sheet online.

I have "arduinoed" a couple of RC cars already. But this new one is a bit of off-roading type, and may require more current than L293d, L298N . That is why I decided to take advantage of the inbuilt controller with good heat sinking.

One side of the board shows my poor soldering skills and hot glue work to attach  and secure a connector to 5 "control - lines" ( @raschemmel   Any better term for this?)

Ajan


raschemmel

Take a look at this post.

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

Paul__B

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

Could have saved a lot of time!

dwightthinker

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


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

dwightthinker

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

Quote
@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 ?

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

dwightthinker

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

Ajan

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.

Ajan



....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
https://www.youtube.com/watch?v=WEGlsztBOPQ&ab_channel=GrishaBaranovskij


Ajan

I am met with a set back on this interesting project a few hours back. :-(
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.  :-( :-(


raschemmel

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

Ajan




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.
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.



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