Model boat DIY speed control problem

MisterBill2

Joined Jan 23, 2018
17,743
Interesting thread here!But I suggest caution as the ZN409CE may not be electrically similar to the other IC, which appears to be more current. In fact, after looking at both sets of application information, they do not appear to be interchangable. So I suggest a very detailed side by side comparison.
 

Jerry-Hat-Trick

Joined Aug 31, 2022
491
The white wire is the signal output of the radio receiver.
Thanks, although I'm not that familiar with how RC radio works. It that a pulse every 20mS with duration from 1.0 to 2.0mS where 1mS would be full speed in one direction, 2mS full speed in the other direction and 1.5mS for the motor to stop? I'm trying to work out how the circuit should work from the sketchy datasheet and the more helpful app note (my post #14) which includes an example of a similar motor speed control circuit
 

Alec_t

Joined Sep 17, 2013
14,201
That post #14 ZN409 App Note refers to the "power amplifier consisting of two external PNP transistors and two on-chip NPN transistors which form a bridge circuit to drive the dc motor". Providing that is true and there are no on-chip active pull-ups on pins 7 and 8 then I think those pins could be used something like this, since the gates ensure the NPN bases are not driven simultaneously :
1696621453592.jpeg
The two NPNs and the Pull-up R5 already on the pcb form an OR gate for the extended PWM pulses.
 

Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
If it helps at all on the RC receiver, this is the system I have. I'm trying to find specs on the receiver output to the servo, or in this case the speed control.

I know old radios use PWM, pulse width modulation. That was with older 72 and 75mhz systems. I don't know what newer 2.4ghz systems would use.

On Monday I will try soldering pin 10 and flip pin 8 out of the socket.

https://www.radiolink.com/at9spro

Maybe also of interest...... https://www.google.com/search?q=radio control receiver servo signals
 

Alec_t

Joined Sep 17, 2013
14,201
I don't know what newer 2.4ghz systems would use.
According to the User Manual your AT9S system is capable of operating in several modes, one of which is PWM. In other brands (at least), the conventional 1ms-2ms pulse width range still appears to be in use in these newer systems.
On Monday I will try soldering pin 10 and flip pin 8 out of the socket.
If your Tx is set for PWM mode and the IC behaves as I now think it likely does, i.e. as in my post #26 simulation, then I reckon with pin 8 open circuit you should get speed control, albeit for one direction only. It will be interesting to know the result.
 

Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
On both, I soldered pin 10 (Ve) and butterflied out pin 8 on the IC so no chance of contact. Pin 8 on the IC socket is still not soldered.

On one of them, I get variable speed in one direction like Alec_t mentioned. Moving the transmitter stick in the other direction nothing happens. I am getting 5 volts out to receiver. I am able to adjust VR1 to center the ESC to the center on the transmitter stick and also adjust VR2 to maximum speed.

On the second one, when I power it up the motor jumps a bit. Output to the receiver is 8.5 volts. So something is wrong there. I don't have enough nohow to determine the problem here.

Link to the schematic
 
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Jerry-Hat-Trick

Joined Aug 31, 2022
491
Sounds like you are getting closer with one of them. I’m wondering, if you butterfly out pin 7 and connect pin 8 instead, does it work in the opposite direction?
 

Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
I butterflied 7 so no connection on pin 7.

I left 8 butterflied out (the socket pin still unsoldered) and used a micro jumper on pin 8 to R3. Yes I get the motor spinning in the opposite direction and the transmitter stick also pushed in the opposite direction.
 

Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
If I have this right, when the transmitter stick is pushed in one direction, pin 7 would spin the motor in a direction and the output of pin 8 would do nothing. If the same stick is pushed in the opposite direction, pin 8 would then spin the motor in the opposite direction and pin 7 would do nothing. So wouldn't both pins need to be soldered in order to give both directions to the motor? Does the internal circuit of the IC work that way or is my statement incorrect?
 

Jerry-Hat-Trick

Joined Aug 31, 2022
491
Yes, I agree. But I’m concerned that when either 7 or 8 go high to drive the motor in one direction the other output goes low so it may not work at all. In the motor speed control example in the application note pins 7 and 8 are left unconnected and pins 5 and 9 are used to turn on transistors T2 and T3

I wonder if it would still work in one direction with either 7 or 8 connected via a diode? If the logic level mosfet still turns on with the lower voltage then both 7 and 8 could be connected via diodes

Just connecting 7 and 8 together would surely just put us back where we started?

And for the issue with the second board, could you swap the ICs to see if the fault follows the IC or the rest of the board?
 
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Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
I had already swapped the IC's but failed to mention that. It's not the IC, something in the board. And I'm getting 8.5v at the red wire output on the non-working board when it should be 5v.

With pin 8 connected/pin 7 not, could I just measure the output of pin 7 to see what it is? And do vice versa
 
With pin 8 connected/pin 7 not, could I just measure the output of pin 7 to see what it is? And do vice versa
Yes, but I expect you will simply read zero volts which won’t really tell you if the pin is grounded. The purpose of a diode is to prevent the active output from being grounded by the other. If the motor still runs with a diode between the output pin and the transistor you may need a resistor to ground after the diode because the transistor doesn’t draw current and the gate needs to discharge between PWM pulses - but try with just the diode
Or maybe a resistor instead of a diode? This might work if half the output voltage is sufficient to turn on the transistor if/when the other output pin is grounded. I’d be reluctant to connect pins 7 and 8 together until having explored alternatives

With 8.5V instead of 5V maybe the 7805 linear voltage regulator is faulty? What supply voltage are you using.
 
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sarahMCML

Joined May 11, 2019
352
I had already swapped the IC's but failed to mention that. It's not the IC, something in the board. And I'm getting 8.5v at the red wire output on the non-working board when it should be 5v.

With pin 8 connected/pin 7 not, could I just measure the output of pin 7 to see what it is? And do vice versa
What do you mean by "getting 8.5v at the red wire output"? Where is that? You're only using a 5V supply, correct?
A quick test: If you adjust VR1, with your transmitter input set at neutral, can you get the relays to stop chattering, then when you got to reverse, get the relays to respond by switching over?
 

Alec_t

Joined Sep 17, 2013
14,201
With pin 8 connected/pin 7 not, could I just measure the output of pin 7 to see what it is? And do vice versa
Yes. One of pins 7 and 8 should be pulsing (a DMM should show an averaged reading of somewhere between 0 and 5V, depending on pulse duty cycle) and the other should show ~0V to ground if my theory of the IC operation is correct. The 0V would indicate that there is no active pull-up on those pins and that they are likely driven by open-collector NPNs, which would tally with the write-up in the App Note. It should therefore be safe to link pins 7 and 8 directly, as your pcb is designed to do.
If you have access to a dual trace 'scope it would indicate clearly if there is any conflict on those pins.
 

Alec_t

Joined Sep 17, 2013
14,201
And I'm getting 8.5v at the red wire output on the non-working board when it should be 5v.
If 8.5V is getting to pin 10 of the IC then the IC could have been damaged. The Absolute Maximum supply voltage for the IC is 6.5V according to the datasheet.
 

Thread Starter

Ken_NJ

Joined Feb 22, 2021
43
A lot was said between you both so not sure how to proceed. I can breadboard off of either pin with diodes and resistors if need be.

8.5v was measured at the red wire output for the receiver which is on top left corner of the diagram. I am able to use both IC's in the more working board so I don't believe either IC is damaged. I have other 7805's, I can try to replace it.

I'm use a 12v source, a sealed lead acid battery for testing. In the boat it will be a pair of 3s LIPO's in parallel.
 
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