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RF Receiver and DC motor running from same power source?

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adamthole

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I've been working on a project for some time now, and I cannot get it done. I am using an RF-KLP receiver, a DC motor, and an HT12D decoding chip. My problem is that when I press the button on my transmitter to turn on the dc motor, the motor turns on no problem. I let go of the button, and the motor stays on. This is because the motor is either a) creating so much noise that the receiver cannot operate properly or b) the motor is sucking so much energy from the batteries that the receiver cannot operate properly. My power source is 3 D cell batteries.

The motor stays on because that is how the HT12D chips operates. When it is out of range it will stay in whatever state it was before it became out of range. I also use another chip that will go all inactive outputs when it is out of range. When I use this chip in the circuit, the motor pulsates on and off.

If anyone knows how to make this work, or has made this work, or would like to try to make this work, please do. I have been working on this for some time now and I really hope I get it done soon.

Thanks
 
the motor creates a lot of noise so controling motor anr electronics from the same supply is not possible. use a voltage regulator and krona(9Vbat) or 3 AA(A) cells for the remote and those D cans for motor
 
As already suggested, you should post your circuit so we can see what you're doing so far. However, one thing which is VITALLY important is to fit suppressor capacitors across the motor - it could well be that the problem is RF borne, rather than a PSU problem. To check this, try feeding the motor section from it's own batteries and see if that helps.

If your only power source is 3 D cells, you don't have much voltage to play with! - generally motors run off higher voltages, and you can regulate down to a lower voltage for the electronics.
 
Here is my schematic. I might have the transistor in backwards on the schematic, but I have it right on my board. (I forget how the symbol works, and I was in a hurry).

The final version would be using relays as opposed to just a transistor, but I figured it needs to work this way first.

I do have caps on my DC motor, and I have tried various other RF noise cancelling things.

It does work with the motor on a seperate power source

On the 5V regulator, a 9V battery would be enough to power it? Wouldn't that wear down the 9V very quickly?

Thanks
 

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When you have a big current draw on a battery (like a motor) it can cause the voltage to drop fairly significantly. If it drops below 5V + the dropout for your regulator it will cause problems with your RF receiver. When the motor turns on it will draw a surge of current (called inrush current) that might reset your RF stuff.

If the inrush current is the problem a big cap and a diode might be enough to keep the RF voltage high enough during the surge.

You could also try 2 NiMH bateries and a boost converter to get 5V. The boost converter should be able to step up the voltage to 5V even if the battery voltage drops.

Using 2 separate batteries will work too.
 
I tried the 9V and the 5V regulator with my test motor and it worked. However, when hooked up to my actual motor, much bigger, it does not work.

I tried it with my actual motor running from a seperate power source and I had no problems.

Any more ideas, for the single power source?


Is their an easy way to multiply my 4.5V and turn it into 9v?

Thanks!
 
Maybe is not a power problem. Measure the voltage at the base if the driving transistor. It is high enough to keep the transistor ON (I think).
If so, put a series resistor of 1K between the IC and the base of transistor and another resistor 4K7 (or any values from 2k2 to 4K7) from base to emmiter.

Now, supose u have a power problem. Use 3 capacitors of 100nf each and connect them in delta form between the motor terminals and ground. These should be close to the motor.
That is 1 from terminal a to b, 1 from terminal a to ground and 1 from b to ground. This performs a sort of filtering.
Further, use ferrite cores around the motor terminals, a torroid one and wound the motor wires about a couble of times.
Another trick is to put 2 series inductors with the motor and 2 capacitors to form a Pi circuit with the inductors.
 
The voltage at the base of the transistor is around 4.9V when it is on. I did the resistor thing you said to do, not sure what it does besides cut down on the voltage applied to the base, and that didn't help anything.

The motor already has the 3 capacitors, but how would that help a power problem. Isn't that more of a noise supressor?
 
adamthole said:
The voltage at the base of the transistor is around 4.9V when it is on. I did the resistor thing you said to do, not sure what it does besides cut down on the voltage applied to the base, and that didn't help anything.

If the voltage on the base is 4.9V, then the transistor has blown (it can't go more than about 0.7V). As already suggested you should have a resistor in series with the base from the IC (check the hardware extras section of my tutorials for diagrams), this will prevent the IC blowing the transistor. You should also have a reverse connected diode across the motor, this prevents back EMF from the motor blowing the transistor, again it's shown on the diagrams in my tutorials (but with a relay, rather than a motor, but exactly the same thing!).
 
Nigel, thanks for the info about the base not being able to have more than 0.7V put into it. I had no idea. However, even though I have been giving it 5, it still works fine at close ranges. What symptoms will the transistor have when it is blown? I do have a diode on my relay, however, what would happen if I didn't? I didn't use a diode on a relay, quite a long time ago, and I never had any problems. Just curious. I'll try to get 0.7V going into this thing.

UPDATE:

Okay, I played around with it a little. Out of curiosity, I put the base of the transistor right to ground (PNP) and the relay clicked. I let go, and it stayed clicked. Transistor fried. I then did the same thing again with a different transistor, but using a resistor, and everything worked out fine. This makes me assume that I never had any problems with a transistor, somehow the chip was acting as my resistor perhaps. I put a resistor from the pin out to the base, just incase.

So, there goes that idea...unless I am missing something. I connected everything, and I still have the same problem. I had an idea of connecting the receiver to the power supply with germanium diodes and putting a big capacitor on the receiver. This way the receiver would not suffer the voltage drop. I haven't been able to test this as I only have silicon diodes on hand and they drop .7 volts, bringing my power supply down to an unacceptable 4.3V on the receiver.

Thanks
 
I don't see where elaborate solutions are necessary.

Add an electrolytic cap in parallel with a ceramic cap on the transmitter, and at least a ceramic cap on the motor as a supressor. There are better supressor schemes but this should be ok.

If things are really bad, you can add an inductor between the power supply+motor and the caps+xmitter, making an LC filter.

If the motor is dragging down the batteries, obviously you either need a fresh set of batteries or perhaps you need a type with more current capacity.

As noted, that transistor needs a base resistor and is almost certainly blown. I would replace it after being used like that.
 
Thanks for the suggestions. I will try that, but I do have some questions. What would an electrolyic in parallel with a ceramic actually do? To me it just seems like it would make the total capacitance less.

Do you have any diagrams of how the inductor set up would look?
 
adamthole said:
Nigel, thanks for the info about the base not being able to have more than 0.7V put into it. I had no idea. However, even though I have been giving it 5, it still works fine at close ranges. What symptoms will the transistor have when it is blown? I do have a diode on my relay, however, what would happen if I didn't? I didn't use a diode on a relay, quite a long time ago, and I never had any problems. Just curious. I'll try to get 0.7V going into this thing.

Without the diode it's VERY likely that the back EMF generated when the relay turns OFF will kill the transistor, you might have been EXTREMELY lucky and your's survived - but it's a VERY high probability that the transistor will be destroyed the first time it turns OFF.

Okay, I played around with it a little. Out of curiosity, I put the base of the transistor right to ground (PNP) and the relay clicked. I let go, and it stayed clicked. Transistor fried. I then did the same thing again with a different transistor, but using a resistor, and everything worked out fine. This makes me assume that I never had any problems with a transistor, somehow the chip was acting as my resistor perhaps. I put a resistor from the pin out to the base, just incase.

Your diagram above showed an NPN transistor, which do the way it's connected is correct - but in either case a base resistor is essential.

What would an electrolyic in parallel with a ceramic actually do? To me it just seems like it would make the total capacitance less.

Capacitors in parallel INCREASE the capacitance, capacitors in series DECREASE it.

Your diagram didn't show much in the way of capacitors?, you MUST have HT decoupling capacitors, and electrolytics are most effective, but adding small ceramic ones in parallel increases high frequency decoupling.

You first need to connect everything up correctly (so try posting the COMPLETE diagram, including ALL components, exactly as wired), and we can make suggestions. Layout could also have a major effect on your problem!.

As I mentioned before, try feeding the motor from a seperate temporary supply, to prove if the problem is via RF or PSU.
 
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