I just purchased 2 Wixels together with Arduino Shields. To get started, I loaded the USB-to-serial APP on one of them and expected it to behave like a normal USB serial adapter. The Wixel is mounted on the shield and powered by USB. Connecting TX to RX produces no echo with any terminal program running on Windows. I then measured the voltage levels on RX, TX to get 0.035V and 0.0.55V, respectively. These are serial inverted levels at idle. I intend to use these shields with a Netduino Plus which is running on 3.3V and uses true serial (e.g. idle high).
So, my questions are:
Does the Wixel employ inverted serial (idle low)?
Given that I will be interfacing to a 3.3V UART, are the ARD TX-WX RX, ARD RX-WX TX shield circuits necessary?
If question 2 is no, where are the jumpers located on the shield?
If question 1 is yes, does this carry over with wireless?
Edit:
N.B. I just read further in the APP description and found the answer to question 1:
“The control signals are all inverted, which means that a logical 0 corresponds to a high voltage (3.3 V) and a logical 1 corresponds to a low voltage (0 V).”
Based upon my measurements, this statement also applies to TX, RX. This does not make me happy. I means that I must use up valuable space on the shield with a 74HC14 Schmitt trigger inverter to get the right logic levels.
You were measuring the pins labeled RX and TX on the shield, and there was no Arduino involved, correct? If so, your measurements sound ok. There are some parts of the shield that don’t work unless you have an Arduino connected. You can see this yourself by looking at the schematic in the Wixel Shield for Arduino User’s Guide. For example, the Arduino RX line is pulled up to the 5V node on the shield, which is supposed to be connected to the Arduino’s 5V. You didn’t supply an Arduino, so that pull-up will not work and you would expect to measure the output as low. The Arduino’s TX line is connected to a voltage divider (2.2k, 4.7k) which is strong enough to overpower the internal pull-up on the Wixel’s RX line that is trying to pull that line to 3.3 V.
No, it uses non-inverted serial (idle high).
No. I just checked the Netduino schematic and it looks like the RX and TX lines are just connected to the chip and not anything else. (On standard Arduinos they are connected to a USB-to-serial adapter.) This is good because you can probably just connect P1_6 directly do the Netduino’s RX and P1_7 directly to the Netduino’s TX. I don’t think you’ll be able to program the board wirelessly without a lot of extra work, but you should be able to at least communicate with a running program wirelessly.
Thanks for the reply. They clarified the issues for me. I cut the smd jumpers, connected P1_6 to P1_7 and in the USB-serial mode the Wixel echos as expected.
Hi beb101,
Did you succeeded on connecting your Netduino+ to a Wixel?
I’m thinking about buying a pair of Pixels in order to wirelessly control a robot from my PC or receive its status report from it… Do you think this would be feasible? Will I need to use the Arduino shield for this?
Yes, they work in either wireless mode or connected to to the PC as a USB to serial adapter. My previous difficulty was with the voltage level shifting on the Pololu shield that David Grayson clarified. The Pololu shield is specifically designed for the Arduino which supplies 5V and to get at the IO pins of the Wixel. You don’t need a shield; just configure the Wixels and hookup one to the PC and the other to the Netduino with 3v3, gnd, Tx and RX. Another very innovative protoshield which will give you much greater flexibility can be found here,
I ordered three of these and they are vey nice for mixed through-hole and surface mount work. Also, if you are looking for longer range take a look at the XRF Wireless modules.
There have been reports of these working at up to 3km on the Picaxe forum and the interface is very easy to work with. They also sell these through the eBay shop and the shipping is reasonable and prompt
My idea is to build a sort of indoor robot with a Rover 5 for the chassis, a RoboClaw 2x5A for controlling the rover’s motors (and decoding the quadrature) and a Mini Maestro for controlling some servos. Everything will be handled by my N+ by using serial commands between the devices.
Since it would be great to also manually control the robot from a PC and getting its statuses, I was thinking in some wireless solution. It seems that Wixel is the most suitable, easy to deploy and cheap solution to achieve this by now.
So here is my last (I hope ) question: In your experience, how far away can two wixels be located without losing quality in the connection? Did you face some problems with walls or physical obstacles?
Due the fact that I live in Argentina and here it’s practically impossible to get such things, I’m planning to make a big order to Pololu and finally get a pack by mail containing everything at once. Import taxes here are ridiculous (50% including shipment) so you can imagine how expensive could that be for me at the end of the day…
I really haven’t used the Wixels farther than a few feet from each other. I mostly use them as a wireless link from a PC terminal to the Netduinio in order eliminate the USB serial adapter cable. In the specs, they claim up to 50 ft (probably in free air), but I would not count on it for a good strong signal. The antenna on the PCB is not optimal to get maximum range and I also recall that they recommend keeping the Wixel 1 to 2 inches above a flat surface. My guess is you could maintain a good signal in the same room, but through walls it would get iffy. To put this in perspective, compare the antenna on your 2.4 GHz wireless router with the printed circuit antenna on the Wixel. If you are placing an order you might also want to look at a nice super flexible USB cable. I haven’t found them elsewhere,
In our tests, we were able to consistently get decent communication up to a range of around 50 ft indoors, through several walls. Ultimately, the range depends on things like the number of walls/obstacles in the way, what they’re made of, how high of a communication rate you need, and even the orientation of the Wixels, and there is also probably some unit-to-unit variance, but that 50-ft spec is meant to give a general (and, we hope, somewhat conservative) idea of what you might expect indoors. We have not characterized their line-of-sight range (is this what you mean by “in free air”?), but we did once try using a single pair of Wixels outdoors and were able to get decent communication at perhaps 200 ft with direct line-of-sight between the Wixels.
Thanks for your clarifications.
50 ft (indoor, in a flat with no more than 1 wall) is more or less the distance I pretend to cover with the Wixel.
The price is good and as per the overall comments, it seems to be a really good choice for a wireless solution.
I’ll give it a try for sure…
) question: In your experience, how far away can two wixels be located without losing quality in the connection? Did you face some problems with walls or physical obstacles?