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Old Apr 25, 2010, 03:42 PM
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Originally Posted by AnnihilaT View Post
Hi Rich,

Here is the DIY scope i was talking about: http://www.sparkfun.com/commerce/pro...oducts_id=9484

The range im testing right now is only a meter or so which is all i need.

Im thinking the issue with the voltage has to do with these module only able to deliver 10 micro amps and i think the futaba radio needs more than that to drive it so im working out how to amplify the signal before it goes into the 9C
Thaks for the link. I'd suggest using your scope to measure pulse voltage as meter readings may be confusing you.

I'm thinking the issue is signal polarity. My modules put out a healthy TTL signal. If not then a pull-up resistor would be an even easier fix. You might want to read the prev response carefully.
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Old Apr 25, 2010, 03:57 PM
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Hi Rich,

Either you are talking over my head and im not getting what you are trying to tell me (very possible) or maybe I didnt explain it good enough. In the possibility of the latter i will try again.

The signal on the scope looks absolutely normal until the moment i connect data out from the RX module to the PPM in pin of the 9C radio. At that point the voltage reading on a multimeter goes from around 4.5 volts down to 0.27volts. Also on a scope, i see the signal go from normal to extremely attenuated. This is why i was thinking it had something to do with internal resistance of the 9C or something alike. My modules also put out a very healthy signal on the scope right up until the moment i connect signal to the PPM-IN pin of the trainer port.
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Old Apr 25, 2010, 05:15 PM
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Originally Posted by AnnihilaT View Post
Hi Rich,
The signal on the scope looks absolutely normal until the moment i connect data out from the RX module to the PPM in pin of the 9C radio. At that point the voltage reading on a multimeter goes from around 4.5 volts down to 0.27volts. Also on a scope, i see the signal go from normal to extremely attenuated. This is why i was thinking it had something to do with internal resistance of the 9C or something alike. My modules also put out a very healthy signal on the scope right up until the moment i connect signal to the PPM-IN pin of the trainer port.
Haven't been following this thread, but thought I'd offer the following since I have a FF9 and have interfaced to it's PPM input quite sucessfully before:-

Are you sure you are connecting to the PPM input pin of the 9C. Here's a diag I used in one of my projects:-

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Old Apr 25, 2010, 05:25 PM
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Hi Ian,

Yes thats precisely how im connecting. Im using the same diagram
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Old Apr 25, 2010, 06:29 PM
7000mw of raw power!
rich smith's Avatar
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Quote:
Originally Posted by AnnihilaT View Post
The signal on the scope looks absolutely normal until the moment i connect data out from the RX module to the PPM in pin of the 9C radio. At that point the voltage reading on a multimeter goes from around 4.5 volts down to 0.27volts. Also on a scope, i see the signal go from normal to extremely attenuated.
I could be wrong. If you connect an active high signal to an active low one you will see a similar effect. Is the PPM in pin same polarity as module out before connecting?

Another issue might be connecting two outputs together. Do you clearly see pulses on one and none on the other before connecting?

Or you might have a damaged unit or wiring error.

One way to test outputs is load it down with a 2k resistor and see if that swamps the signal. The same trick can be used to check inputs too.
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Old Apr 25, 2010, 07:45 PM
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I made a quick video to show what im doing.

ASK RX module and a Futaba 9C (4 min 49 sec)
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Old Apr 26, 2010, 01:15 PM
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Originally Posted by AnnihilaT View Post
Hi Ian,

Yes thats precisely how im connecting. Im using the same diagram
So just to clarify.....you are using pins 2 (com) & 6 (ppm into 9C).....correct?

Ok, so I would then suggest you disregard to 9C for now and load up the output of your receiver and see how that is affected by load.

I'd guess it should be able to handle a 4k7 load without problem......possibly even lower.

If you find that a 100k load or bigger is giving you the huge voltage drop then there's a problem with the receiver.

You could also switching off the 9C and with NOTHING connected to the PPM port measure the resistance between pins 2 & 6. What this will do is record the input impedance of the 9C......maybe it's near dead short!
I measured my FF9 and it's 18.6k.

Ian.
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Old Apr 26, 2010, 01:57 PM
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Originally Posted by IanJ View Post
So just to clarify.....you are using pins 2 (com) & 6 (ppm into 9C).....correct?

Ok, so I would then suggest you disregard to 9C for now and load up the output of your receiver and see how that is affected by load.

I'd guess it should be able to handle a 4k7 load without problem......possibly even lower.

If you find that a 100k load or bigger is giving you the huge voltage drop then there's a problem with the receiver.

You could also switching off the 9C and with NOTHING connected to the PPM port measure the resistance between pins 2 & 6. What this will do is record the input impedance of the 9C......maybe it's near dead short!
I measured my FF9 and it's 18.6k.

Ian.

Yes, i am using pins 2 & 6. I measured input impedance between these two pins and it was at 19.87k. This was with a length of wire attached to the pins so that probably explains the small descrepancy.

Did i mention that in the datasheet of this receiver it mentions that for logic HIGH and logic LOW ILoad = only 10 uA (micro amps) ? Im too new to this to know exactly how to calculate that into the equation but im pretty sure that this is way too low for 18.6k input impedance? Or am i talkin' crazy ?

BTW: here is a link to the datasheet - http://www.sparkfun.com/datasheets/W.../MO-RX3400.pdf
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Old Apr 26, 2010, 02:08 PM
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Originally Posted by AnnihilaT View Post

Did i mention that in the datasheet of this receiver it mentions that for logic HIGH and logic LOW ILoad = only 10 uA (micro amps) ? Im too new to this to know exactly how to calculate that into the equation but im pretty sure that this is way too low for 18.6k input impedance? Or am i talkin' crazy ?

BTW: here is a link to the datasheet - http://www.sparkfun.com/datasheets/W.../MO-RX3400.pdf

Tada!................

You 9C load is just over 250uA............much more than your receiver can handle.

You need to buffer the signal......and to do that you'll need a bit of electronics knowledge. Many different ways from a couple of transistors (fets have lowest gate current) and a few resistors, to a simple 74HC04 (2 gates in series).

Ian.
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Old Apr 26, 2010, 02:37 PM
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Something like one of these two options? And would both of these work and produce the same results?
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Old Apr 26, 2010, 02:53 PM
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That will certainly buffer the signal. Remember to tie unused inputs high. I would be very surprised if that were the problem. Please report back results.
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Old Apr 26, 2010, 02:53 PM
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Originally Posted by AnnihilaT View Post
Something like one of these two options? And would both of these work and produce the same results?
Yes that would work. Just make sure you buy 74HC04 and not 74LS04 for example.........much less input current.

Ian.
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Old Apr 26, 2010, 04:58 PM
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@rich, of course i will report back the results

@Ian: i googled it but couldnt really figure out the difference between the LS and HC other than a wiki article about the 7400 series of IC chips that says that KS is low speed and HC is high speed? Can you explain to me the difference between the two as you understand it?
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Old Apr 27, 2010, 07:01 AM
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Originally Posted by AnnihilaT View Post
@rich, of course i will report back the results

@Ian: i googled it but couldnt really figure out the difference between the LS and HC other than a wiki article about the 7400 series of IC chips that says that KS is low speed and HC is high speed? Can you explain to me the difference between the two as you understand it?
Generally, very generally, the input current of a LS series logic gate can be 40uA, whereas the same for HC or HCT series is about 1uA.

I think your cutoff is 10uA........however, if you have an LS04 lying around then try it......different manufacturers will give different results. You might be lucky.

There are many ways to buffer your signal........but if you ain't too hot at electronics then the above is your way forward.....just 1 component, give it +5vdc power and off you go.

Ian.
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Old Apr 27, 2010, 02:37 PM
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Originally Posted by IanJ View Post
Generally, very generally, the input current of a LS series logic gate can be 40uA, whereas the same for HC or HCT series is about 1uA.

I think your cutoff is 10uA........however, if you have an LS04 lying around then try it......different manufacturers will give different results. You might be lucky.

There are many ways to buffer your signal........but if you ain't too hot at electronics then the above is your way forward.....just 1 component, give it +5vdc power and off you go.

Ian.
Good explanation Ian, in terms i can understand Thanks!
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