Bioloid I/O interface

[Joe]

At $50, the MEGAbitty seems a bit pricey. What about the Pololu Baby Orangutan ($25 in single quantities). Half the price, smaller, and available with either mega48 or mega168.

I don't work for Pololu, and I haven't tried this product yet... but I've always been very happy with Pololu's other products.

Best,
- Joe

[pepperm]

The Orangutang looks good too, and it's cheap but to be honest by the time we get it here in the UK it costs the same in pounds as it does in dollars which is bad, especially when the exchange rate is almost 2 for 1.

I can't help thinking though that with all these boards we will still need a daughter board with connectors and the 1 wire interface on it, which sort of defeats some of the objective.

What I would like to produce is a single small, single sided board that people can make at home or we can mass produce very cheaply, either populated or bare. I did some quick investigation on the web and concluded that it would be cheaper to buy the likes of the Orangutang or megabitty though.

What I'll do is see if I can produce a small single sided board and if anyone has any suggestions as to how and where we could get this produced cheaply I would like to hear from them. Say 20x40mm, single sided (maybe double) with maybe 50 pads and a silk screen.

Don't forget that we still need software though, without that we have nothing.

Mark

[pepperm]

I found the Orangutang here in the UK if anyone is interested http://www.technobots.co.uk/index.html?lang=en-uk&target=d729.html

about £20-25 depending on model and postage and VAT. See what I mean about prices!

[pepperm]

I've knocked up a small daughter board that is intended to solder over the top of the Orangutan board from Pololu. There are two versions in the ZIP here
http://robosavvy.com/Builders/pepperm/PololuDaughterV1.x.zip
One for components mounted on the bottom of the board (V1.2) and one for components on the top (V1.1). It depends how you want to solder the 1wire bus connections and the pass through pins you see. They are in Eagle format, single sided with just 2 jumpers per board.

The board is designed to have long pins coming out of the top of the Orangutan board, through into the daughter board. The same should happen with the programming pins and ADC7. I didn't bother with the VCC pin as it is on the programming connector too. There is a pad to indicate a 4mm hole to be drilled to allow access to the variable resistor below on the Orangutan board.

I don't have an Orangutan board yet so can not 100% vouch for the board, but it looks OK so far. I have had to align everything with the pictures on the Pololu site so I hope they haven't changed the board design.

The whole thing should now be 18 x 30 x about 10mm when constructed.

Mark

[Joe]

Wow, that's tiny! Sounds great!

One word of caution — please distinguish between Orangutan and Baby Orangutan. The former is a lot bigger and more expensive, and might turn some new readers off if they don't realize you mean the tiny/cheap board.

Best,
- Joe

[pepperm]

Yep Everyone. Joe is right, we are talking about the baby Orangutan (-0216 http://www.pololu.com/products/pololu/0215/), and the Mega128 version at that - it has more memory.

Mark

[limor]

Hi,

I've updated my code for the Pepper Board V1.
The code now also reads from an analog input port PC0 (ADC0).
If you send the command PING to the board address it responds with an empty packet.
If you send the command READ to the board address, it responds with the value of the voltage on ADC0 which is in reference to VCC at AREF pin.


http://robosavvy.com/site/Builders/limo ... 2Mar07.zip

[limor]

Did a little experiment today and connected the PepperV1 board to a Kondo KRG3 gyro. (picture says krg2 but it is a krg3)



Then connected it to the PC and sampled the values at 100hz through our CM5-Simulink setup. Ran the samplling and shook about the KRG3.

The results were quite surprizing.



seems like the values change at a rate of 0.4hz. After looking at the Japanese paper that comes with the KRG3, there is a 0.4hz mentioned there, whatever that means, probably has to do with the refresh rate..

I'll wait for the SparkFun gyro boards that will be available on RoboSavvy store this Tuesday.. although just discovered that the Vref of the IDG-300 is 1.23V but on the Pepper board V1, the AREF input on the Atmega8 is soldered to VCC which means out of 10 bit of ADC i get only 8 bits of information. 8 bits should be enough to work with.

[limor]

Actually that was caused by a bug

The KRG-3 refresh rate is very fast!


here you can see the DC value (no rotation) at about 280. Clockwise rotation (when looking at the KRG3 from the front, goes up to about 750 and anticlockwise goes down to 0. Which makes sense because on that Japanese sheet that comes with the KRG-2 it says that the DC is 1.35V so since our Pepper Board V1 runs at 5V with 10 bits of ADC resolution, (1.35/5)*1024 = 276

we (user rustyarmor + me) took it a step further and let the Bioloid swing while measuring the gyro..


perfect decaying sinusoidal we could actually measure the friction on the hands.
Here's a phone clip of happy engineers at 3am.



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<PARAM name="PLAY" value="true">
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And here he is swinging in sync with his 3D avatar in Simulink

phpBB [media]

Here is a rar file with the CM5 code and the low-level serial device driver S-function that is needed in order to allow Simulink/Matlab Real-Time-Windows-Target to talk with the CM5 while XP is running in "close to real-time" mode.

[pepperm]

on the Pepper board V1, the AREF input on the Atmega8 is soldered to VCC which means out of 10 bit of ADC i get only 8 bits of information. 8 bits should be enough to work with.

Limor

How would you like the AREF input connected? I will look at changing the design for you.

Mark

[limor]

on the Pepper board V1, the AREF input on the Atmega8 is soldered to VCC which means out of 10 bit of ADC i get only 8 bits of information. 8 bits should be enough to work with.

Limor
How would you like the AREF input connected? I will look at changing the design for you.
Mark

It should be disconnected and exposed as a through-hole or pin. This would allow to attach to a reference maximum voltage without changing any code and thereby getting the full 10 bits of ADC resolution. I think that with careful hands, it is possible to detach the AREF pin on my V1 board and allow to connect it to an external reference voltage.

[edit cont'd]
I just looked at the datasheet of ATMega8 and found this about reference voltage options:
Internal reference voltages of nominally 2.56V or AVCC are provided On-chip. The voltage reference may be externally decoupled at the AREF pin by a capacitor for better noise performance.

Therefore in the case of the V1 board in combination with the KRG3 (that unlike the Sparkfun boards, does not expose its own reference voltage of 1.35V), it makes sense to just change the code and reference the chip's internal 2.56V and so get 9 bits of ADC information which is more than plenty. There's no capacitor on the AREF (port 21) as suggested by the datasheet but hopefully there wont be too much noise.

In future versions of the Pepper board, these issues should be taken into consideration.

[pepperm]

In future versions of the Pepper board, these issues should be taken into consideration.

Yes of course, no problems. The board was made quickly to allow comms code to be written and that it has done very well I think.

Mark

[limor]

Yes of course, no problems. The board was made quickly to allow comms code to be written and that it has done very well I think.
Mark

I didn't mean to criticize the board in any way.. the board is perfect for testing comms code!

[pepperm]

No criticism taken, it's nice to get constructive feedback and your observations were constructive. I have no problems with that.

If I make a pin available should it have a capacitor to ground and what value should it be?

I looked at manually moding the board by cutting tracks etc but you would have to isolate that pin then re-connect all the tracks that did go into it, to each other again (as they are the +5V supply line).

Have you seen a sparkfun board yet because I was wondering how the pin can be accessed on that board.

I'll also look at the Orangutan board because I have 2 of these now. I could do with one of the analogue gyro boards too to look at so please give me a shout when you have some. My accelerometer gives pulse width outputs.

Mark

[MOHIT JINDAL]

I am very late. You gurus hacked Ax12+ 6 years back. but ax12+ has only one 74HC126D and two SUF2001. I want to know how both ic connected to atmega 8a chip. Anyone have updated schematic ?