Pololu 23201 Problem!

Hi,there is a strange thing about my Pololu 23201a. When I do my test on my breadboard, I can hear a little noise from the 23201a. If you do not listen carefully,you will not notice it. I connect the 23201 with qik 2s9v1 and the latter can recieve and send commands. But the nosie confused me and I do not think it is good for my test. I power 23201a 4.5v. Once it is powered,the noise is always there. Any advice will be appreciated.

Hello.

Can you measure how much current the RS-232 adapter is drawing? The chip on there has a charge pump that uses capacitors to generate the higher and negative voltages. The ceramic capacitors can have some piezoelectric effect, so they could vibrate a bit. I don’t remember the charge pump frequency off the top of my head, but I think it depends on your load and the supply voltage. If your current is reasonably low, and everything is working, your board is probably fine.

- Jan

Hi, Thanks for your reply. I measure the current that the RS-232 is drawing is 0.03 mA. From the product page I know the supply current is 2mA. I do not understand what my measured value means. There are other strange things.

  1. When the supply voltage of the RS-232 adapter drops from 4.5v to 3.0v, the noise becomes less.
  2. If I connect the RS-232 adapter with one Pololu 2s9v1 qik, the qik can recieve and send commands through it normally.
  3. If I connect the RS-232 adapter with two Pololu 2s9v1 qiks, the two qiks will only recieve commands from the computer (for example, the motors linked with 2s9v1 can rotate if I send command bytes like"0xAA 0x01 0x08 0x2F 0xAA 0x02 0x08 0x2F"). But any of the two qiks will send return data to the computer interface if I want to get the return parameters sent by the two 2s9v1 qiks . I am sure that the AND gate I am using in the hardware circuit work well.

I am looking forward your answer.

The noise changing with voltage is to be expected since the frequency can change, putting things closer or farther from resonance and possibly just moving the frequency out of your hearing range. The other problem really sounds like you don’t have things hooked up correctly: once you are able to do bidirectional communication with one qik, the adapter is working. If you continue having trouble with sending data back, perhaps you could post a picture of your setup and a schematic of the relevant circuit. The 0.03mA sounds like a measurement error, but since it’s low and things are working, I wouldn’t worry about it.

- Jan

Hello,jan

I am a newer about this. With the help of my friend, I measure the supply current again by high precision digital multimeter,it is 0.485 mA. Besides, it is also found that there are something wrong with one of the five resistors on the kit. Its resistance should be 10K,but it is measured 173.I do not know if it is related to the noise.

I post a picture of my setup. The logic voltage of Qik 2s9v1 and supply voltage of my RS-232 adapter is 4.5, and motor supply voltage is 12v. In the picture, I do not connect with the four small DC motor of which the rated voltage is 12v and the rated speed is 12rpm.The type of AND gate is CD4082B and the relevant picture is added.



0.5 mA sounds okay, and measurements of resistors that are in a circuit are unlikely to be accurate, so I wouldn’t put much stock in the 173 measurement. As I’ve said, a little noise is not necessarily indication of anything wrong, and your adapter worked fine for talking to one motor controller, so the only issue left is most likely your circuit. Can you post a schematic so we can see what your intent is?

- Jan

Hello,jan

I have uploaded two pictures in the last post. One is about my setup, and another is about my AND Gate.They are GIF format pictures. Can’t you view the pictures? It is wired.I also find them in my User Control Panel.My registert accout is Lily, and the key is ***.You can log in my account and view them.
Thanks for your immediate reply.

I see your pictures; I was asking for a schematic so we can see what you’re intending to do and your implementation.

By the way, you shouldn’t be posting your password.

- Jan

Hello,jan

I am sorry for doing that


. I am so anxious because the problem delays my work so long. I add a new schematic about my
implementation. In fact,the setup in the schematic worked well before.There are ten qiks in my project to control 20 DC motors. You say the nosie may be related to its load. I do not know if it is due to so much DC motors.

I’m not sure why you took your pictures down since both the intent shown by the schematic and the implementation shown in the pictures could be helpful. Anyway, your schematic looks reasonable, though splitting your TX line ten ways might be pushing it. You might also simplify this to work with two or four motor controllers first. Is your problem still that transmission works, but receiving from the motor controllers doesn’t? Do you know what changed between the time it “worked well before” and now? In the case when you try just two units, make sure you’re pulling the other AND gate inputs high to effectively make it a 2-input AND gate.

- Jan

Hello.

My RS232-adapter can only send command bytes and do not receive data now. If I power the adapter and connect its TX pin and RX pin together, I can not receive the same data I send back. Do you think that the RX pin is damaged in this situation? But, do no worry about me. I buy a new adapter to displace it and now the new adapter connected with ten 2s9v1 qiks work well. I just want to know what happen to my former 23201 adapter and my setup. So, another question is what do you mean when you say that “splitting your TX line ten ways might be pushing it”? Can you explain it in detail? Any advice will be appreciated.

Thanks for all your reply.

I guess the RX pin of your old adapter got damaged somehow (common ways to do that are applying a bad voltage or zapping it with a static discharge).

The comment about splitting TX ten ways is about how you have the same signal going to ten inputs. Each input puts some kind of a load on an output, and more than about five or six inputs per output makes me a bit nervous. The details of if it will work will depend on things like your wire lengths and baud rates. If you have an extra AND gate sitting around, as in your example schematic, you could use the AND gate to buffer your signal (just connect the other inputs high). You could have the TX line from the adapter go to five motor controllers and the AND gate, and the output from the AND gate could go to the other five motor controllers. A general term you can search for if you want to learn more is fanout (or fan-out).

- Jan

Hello, Jan

I follow your advice and correct the old schematic and add it in the attachment. You can see if I understand what you say in the last reply.

Thanks again.