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Old May 30, 2010, 04:56 PM
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[QUOTE=Daniel Wee;15202939]magnetman,

The DOSD+ still draws power from the input side of the Deans due to the way it is connected. To get around this:-

1. Remove completely the solder bridge that was added when initially modifying the sensor board
2. Check that there is no continuity between the voltage output wire of the board to the positive tab of the input port (Deans)
3. Solder a piece of insulated wire or enamel-coated magnet wire from the positive tab of the output port (Deans) to the voltage output wire

This should cause the DOSD+ now to be powered off the output side of the Deans.

Hi Daniel,

Mod done, but this makes no difference. With no load, there is no output from the sensor as expected. With my standby load of about 600ma, there is 8.7 millivolts output from the sensor into the DOSD, measured between GND and sensor output on the DOSD and again on the sensor board itself.

As soon as load gets above this, the DOSD will start to come off zero and start reading current.
It appears some sort of offset required??

Thanks again for your help!

Best wishes Richard
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Old May 30, 2010, 05:08 PM
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Quote:
Originally Posted by Daniel Wee View Post
galaxiex,

I think this is the part:-

http://sg.farnell.com/honeywell-s-c/...sor/dp/1751290

It's kinda expensive but you may be able to get it (HSCMRNN001PG2A3) cheaper from Mouser or Digikey. The connections are pretty straight forward. There are 8-pins but only four are in use, and these correspond directly to the pins from the I2C header on the DOSD+ board. The only thing to do is to add a 0.1uF and a 1uF capacitor across the Vcc and Gnd pins. The exactly pinout can be found on Table 8 in the datasheet (attached).

You should find out how to correctly hook up the pitot system (DIYDRONES sells a kit). I should mention that setting things up for CAS (compensated air-speed) isn't as easy as most people think. On the upside, though - you probably don't need too much absolute accuracy, just relative accuracy would do.

For the barometric sensor, just grab one from Sparkfun (BMP085) or from DIYDRONES (SCP1000-D11 - do not get the SFE one, it won't work). As with such sensors, you need to mount them inside porous foam/sponge and place it where it is equalized with ambient pressure.

Daniel

Thanks Daniel, That helps alot!

I will see if I can find that HSCMRNN001PG2A3 sensor somewhere. (I had trouble trying to order from Farnell before).

No problem about the cap, I understand decoupling capacitors and probably have something suitable in my stock.

Hookup looks easy from the data sheet.

I already have the BMP085 baro sensor and it seems to work great, and I have the pitot tube kit from DIYdrones as well.

For the airspeed accuracy, just relative should be fine.

Thanks again, I'll let you know how it goes.
Dale

Edit; I have the sensor HSCMRNN001PG2A3 coming from DigiKey for 53.17 shipped.
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Old May 30, 2010, 11:28 PM
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magnetman,

Can you check what your Current offset setting in the menu is set to? It should be 0.00.

Daniel
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Old May 31, 2010, 04:14 AM
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Hi Daniel,

Yeah it is Zeroed OK, I tried adjusting it + wise and just made it worse.

Richard

Anyone else had the same problem??
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Old May 31, 2010, 04:23 AM
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magnetman,

Okay, let me investigate this a bit.

Daniel
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Old May 31, 2010, 04:36 AM
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magnetman,

I'm looking at what you posted about your measurements, that you are seeing 8.7mV for 600mA idle current. That is incorrect. The sensitivity of this board is around 12.65mV per 22mA or 0.575mV per mA. By this calculation, 600mA should yield an output voltage of approximately 345mV, not 8.7mV. So something is definitely amiss here.

Here is what I would check first - make sure that the following resistor has been removed as per the photo:-
http://forum.tsebi.com/download/file.php?id=709

Let me know if that resistor is already removed on your board.

Daniel
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Old May 31, 2010, 07:21 AM
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Hi Daniel,

Yes the resistor is removed, but my readings are taken direct from the sensor so it is a sensor problem by the look of it, the output voltage is far too low it seems.

so, for 600ma that would produce only 300 microvolts across two 1 milli- ohm resistors in parallel, (if my workings out are correct)there are two of these on the sensor board.

The chip must be some sort of differential / instrumentation amp with a gain setting ?? There is only one SMT resistor now on the board by the chip, the others are removed as per the original mod. maybe something to do with that.

Here is another conundrum, the calibration figures are not far out for me to get the correct current reading on 24 amps... so maybe the output is only small and not as you say it should be??

Don't know if you have a circuit diag of the sensor available,?? I will poke around and see if I can draw it out.

Richard
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Old May 31, 2010, 07:34 AM
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magnetman,

I've attached the datasheet containing the schematics. The voltage divider has been removed. You can verify if your sensor is working just by measuring the voltages present.

Daniel
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Old May 31, 2010, 09:40 AM
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Thanks Daniel, good info. I changed RL for 100 K and it has increased the output a bit, and the DOSD now reads 100 milliamps, but still 400 or so short.
So now I am getting 10 mv per 600 milliamps, nothing like it should be, but I cannot see anything obviously wrong.

Oh well, looks like I will have to fix up the original Dragon current hall effect sensor until I can figure out what is going on..
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Old May 31, 2010, 09:44 AM
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magnetman,

Any chance you got the polarity wrong somewhere? Deans? Or may be got solder onto the shunt resistor? A solder bridge somewhere? It sounds like your sensor might be damaged.

Daniel
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Old May 31, 2010, 09:52 AM
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magnetman... did you update the firmware of your OSD? And also I will have pcb's arriving in about a week from there on I begin assembling them. Send me your mailing address again to jmstech1@gmail.com, I let you try one out.... consider yourself as a beta tester for us.

John
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Old May 31, 2010, 10:20 AM
Fly the Discombooberator!
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Hiya John/ Daniel, I have had a careful look around at the resistor connections, reflowed the solder but it all looks good. I will try and measure the volts across the resistor with a few amps load , that will tell me a lot. Also had a good look at the chip, all looks OK.

firmware is currently 8.3, will update to 8.4, just in case. Be a pleasure to be a beta tester - will reply to you mail John
Cheers

Richard
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Old May 31, 2010, 08:31 PM
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magnetman,

I think the key is to verify that the sensor output corresponds to the datasheet specifications, especially in terms of sensitivity. This testing will be separate from the DOSD+ as you can test it independently. Firmware is not going to make much difference at this point as nothing has been changed on that front for quite a while.

Daniel

Old sarum - that's Canterbury right?
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Old May 31, 2010, 09:35 PM
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hi daniel.. well upgraded firmware from 6.7 to latest 8.4..
i can toggle to the menu but cannot select to make the changes..

see vid..
MOV00950.MPG (0 min 48 sec)
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Old May 31, 2010, 10:20 PM
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barok,

Most likely your channel assignments for the ailerons and elevators are wrong.

Daniel
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