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Old Mar 28, 2010, 11:51 AM
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bracky72's Avatar
Charles Town, WV
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Does the flytron current sensor work with dosd+ without modification?
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Old Mar 28, 2010, 01:19 PM
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It should - the DOSD+ was designed to work with different types of sensors. The thing with this is that the sensor is a 5V AC current sensor. That is to say, that at 0A current, the output is at 5V/2 = 2.5V. The correct or better device to use is the ACS755 which is a DC (unidirectional) sensor such that you won't waste all the dynamic range.

Secondly, the device has a sensitivity of 40mV/A and the DOSD+ is a 3.3V device. As such the range available is from 2.5V to 3.3V on the sensor or 0.8V which translates to about 20A. That's all you can measure with this sensor using the ACS754 part. Personally I think it is a mistake to use the ACS754. Melih should have gone with the ACS755 and you'd end up with a must higher resolution measurement and better dynamic range and lower noise.

So, in summary - yes, it can be used but you can only measure up to about 20A or so. If you change the sensor and replace it with the ACS755-050, you will be in a much better position. The 0A output is 0.6V and the sensitivity is 60mV/A. This means that you can use 0.6V to 3.3V or a dynamic range of 2.7V, which translates to 45A.

The DOSD+ allows you to configure the zero current output voltage as well as sensitivity so you can pretty much configure it to use any sensor but some will work better than others as explained above.

I should add that if you are willing to make some simple modifications, you can improve the measurable current range a bit. For example, if you insert a series diode in the Isense (current sense) line, you would drop the zero current voltage by the forward bias voltage of the diode. So if the bias is 0.7V (which is quite common for normal silicon diodes, not Schottky diodes) the whole thing now changes. The zero current output now becomes 2.5V-0.7V = 1.8V. So you can use 1.8V to 3.3V or a 1.5V dynamic range. At 40mV/A, this translates to about 37.5A max current measured. Putting two diodes in series improves this further - giving about 55A range. If you intend to do this, you should verify the forward voltage drop of the diodes and make the necessary calculations.

Having said all that, the SFE current sensor is has a much cleaner and smoother output making it a much better candidate as a current sensor, in my opinion.

Daniel
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Old Mar 28, 2010, 04:06 PM
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JMSTECH's Avatar
Canada, BC, Duncan
Joined Dec 2006
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In case you guys missed this SFE current sensor that Dean made, then here it is again. It's cheap, tiny and easy to mod for your Dragon OSD+.
Note: Remove the 3 resistors and run a solder bridge across the resistor pads, joining them all together but only to the pads facing the center of the board.

John
Current Sensor Mod for Dragon OSD Plus (3 min 25 sec)
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Old Mar 28, 2010, 05:25 PM
my karma ranover my dogma
galaxiex's Avatar
Edmonton,Canada Eh
Joined Jun 2007
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Say guys...

How do I use the DOSD+ audio output if I want to also use a microphone?

Can I just "Y" them together and feed both to the vid Tx, or do I need a buffer of some sort?
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Old Mar 28, 2010, 09:44 PM
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Canada, ON, Toronto
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other than the dragon link receiver and trans..what other receiver that can be purchase without modding.. my tx is a futaba 7c..
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Old Mar 28, 2010, 09:59 PM
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Joined Aug 2005
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Barok,

I should mention Thomas's LRS as well but that's like DragonLink. As for the other receivers, you should look at this list:-

http://paparazzi.enac.fr/wiki/Other_....2FC_Receivers

These are all receivers that are already have documented PPM output pins. While you are at it, you might as well look for a receiver that also has a documented RSSI output. That way you can kill two birds with one stone.

Daniel
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Old Mar 28, 2010, 10:00 PM
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galaxiex,

Yes, just "Y" them - tap it in. This should not present a problem to the microphone signal. And don't forget to let us know how it works out.

Daniel
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Old Mar 28, 2010, 10:29 PM
my karma ranover my dogma
galaxiex's Avatar
Edmonton,Canada Eh
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Quote:
Originally Posted by Daniel Wee View Post
galaxiex,

Yes, just "Y" them - tap it in. This should not present a problem to the microphone signal. And don't forget to let us know how it works out.

Daniel
Thanks Daniel!

Def will let you know....

Dale
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Old Mar 29, 2010, 03:40 AM
MelihK's Avatar
United Kingdom, England, Canterbury
Joined May 2008
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Quote:
Originally Posted by Daniel Wee View Post
It should - the DOSD+ was designed to work with different types of sensors. The thing with this is that the sensor is a 5V AC current sensor. That is to say, that at 0A current, the output is at 5V/2 = 2.5V. The correct or better device to use is the ACS755 which is a DC (unidirectional) sensor such that you won't waste all the dynamic range.

Secondly, the device has a sensitivity of 40mV/A and the DOSD+ is a 3.3V device. As such the range available is from 2.5V to 3.3V on the sensor or 0.8V which translates to about 20A. That's all you can measure with this sensor using the ACS754 part. Personally I think it is a mistake to use the ACS754. Melih should have gone with the ACS755 and you'd end up with a must higher resolution measurement and better dynamic range and lower noise.

So, in summary - yes, it can be used but you can only measure up to about 20A or so. If you change the sensor and replace it with the ACS755-050, you will be in a much better position. The 0A output is 0.6V and the sensitivity is 60mV/A. This means that you can use 0.6V to 3.3V or a dynamic range of 2.7V, which translates to 45A.

The DOSD+ allows you to configure the zero current output voltage as well as sensitivity so you can pretty much configure it to use any sensor but some will work better than others as explained above.

I should add that if you are willing to make some simple modifications, you can improve the measurable current range a bit. For example, if you insert a series diode in the Isense (current sense) line, you would drop the zero current voltage by the forward bias voltage of the diode. So if the bias is 0.7V (which is quite common for normal silicon diodes, not Schottky diodes) the whole thing now changes. The zero current output now becomes 2.5V-0.7V = 1.8V. So you can use 1.8V to 3.3V or a 1.5V dynamic range. At 40mV/A, this translates to about 37.5A max current measured. Putting two diodes in series improves this further - giving about 55A range. If you intend to do this, you should verify the forward voltage drop of the diodes and make the necessary calculations.

Having said all that, the SFE current sensor is has a much cleaner and smoother output making it a much better candidate as a current sensor, in my opinion.

Daniel
Hi Daniel,

A small fix about your calculations.

Yes ACS754 gives 2.5V with 0A this is staring point but you are going to wrong direction when calculations amper/volts

Because: ACS754 using industrial bi directional mesurment system, this is why it starts from 5V/2 = 2.5V. I'm using negative direction. This is right way for this type sensors for low voltage applications and all new type industrial sensors using negative direction.

This is right table
0A = 2.5V output
25A = 1.25V output
50A = 0V output

You can use it with your 3.3V system
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Old Mar 29, 2010, 04:01 AM
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Romania, Dolj, Craiova
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I wonder how you get stabile reading with these sensors... For me was a failure with ACS755, the value jumps randomly when you have more than 5A consumption.
However, the 0A 2.5V point and small value are stable. No filter can fix this, tried even 100kOhm with 10microF.
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Old Mar 29, 2010, 05:07 AM
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mark hitchman's Avatar
New Zealand
Joined Sep 2009
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It arrived

My DOSD+ arrived today, I must say it is tiny, I knew it would be small by the dimensions but I am amazed at the size. Could not wait to get a usb to ttl converter freight is slow and/or expensive to New Zealand) so I used a max232 chip and a usb serial converter to connect to the DOSD+, worked excellent. The guide I followed is
http://www.seattlerobotics.org/encoder/aug97/cable.html

Next thing I need is a current/voltage sensor, I will probably have to order one of those as I have no idea how to make one. My gps will be here any day from flytron, I ordered it for my rvosd but I will hook it up to DOSD+ first. Will use a corona rp8d1 receiver hopefully.

Mark
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Old Mar 29, 2010, 06:08 AM
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Joined Aug 2005
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Mark,

Great to hear that - and can't wait to find out how it all goes for you.

Renatoa,

This is the reason why I recommended the SFE current sensor instead. The ACS7xx sensors can be made to work but you will need to filter the output of the sensor extensively, either in hardware, software, or both. If you are sampling the current sensor - bear in mind that some of your ESC's are switching at 20kHz and so your sampling rate should be much higher than that if you want to get a correct reading and avoid aliasing problems.

Melih,

Ah, yes - you connected it the other way around. That would work, and is actually quite clever. The present DOSD+ code assumes normal polarity though. I suppose I can allow the user to use negative polarity but this does complicate things a bit for them. If there is enough demand, I will add this ability.

Daniel
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Old Mar 29, 2010, 06:31 AM
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Romania, IS, Iasi
Joined Nov 2008
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New movies with DOSD+ in action ?
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Old Mar 29, 2010, 06:33 AM
MelihK's Avatar
United Kingdom, England, Canterbury
Joined May 2008
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Quote:
Originally Posted by Daniel Wee View Post
Melih,

Ah, yes - you connected it the other way around. That would work, and is actually quite clever. The present DOSD+ code assumes normal polarity though. I suppose I can allow the user to use negative polarity but this does complicate things a bit for them. If there is enough demand, I will add this ability.

Daniel
You should do this for all sensor inputs because most of quality sensors uses "Ratiometric output" like alegro on sensor market.
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Old Mar 29, 2010, 06:38 AM
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The Netherlands, Utrecht, Amersfoort
Joined Oct 2004
2,193 Posts
I have this Parallax prop plug. Can this be used to update firmware?
http://www.parallax.com/Store/Microc...8/Default.aspx
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