M4 Receiver - 315MHz 1096 Data Pin Questions

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Terrormaster
 
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M4 Receiver - 315MHz 1096 Data Pin Questions

Post by Terrormaster »

Hi, I have a 1096 on order but haven't received it yet. In the interim I've been preplanning my circuit. I want to use the 1096 to drive a simple electromagnet off the same power source (which will be 6v DC). I'm trying to determine whether or not to use a TIP120 transistor in between the electromagnet and the 1096. I couldn't find any documentation on the voltage coming off the DATA pins. Are they the same as whatever voltage I use to drive the 1096? And in addition to using a diode across the leads of the magnet is there anything else I should do to protect the 1096 from induction? Should I diode the data pin as well?

I'm getting the momentary version of the 1096 so the magnet should only be getting pulsed whenever the button is pushed. But that coil is sure to heat up if some jackhat holds down the button too long. I know I could wire in a 555 timer in single shot mode to insure only a pulse happens but I'm trying to keep things simple.

Thanks,
-TM

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adafruit_support_mike
 
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Re: M4 Receiver - 315MHz 1096 Data Pin Questions

Post by adafruit_support_mike »

The datasheet doesn't have any specs for the current capacity of the output pins, but I doubt they'd be able to drive a solenoid directly. It would probably be a good idea to use the transistor or a mosfet.

Either way, you won't need a diode on the line that controls the transistor. The current path for the control signal will be independent of the current path through the solenoid.

Terrormaster
 
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Re: M4 Receiver - 315MHz 1096 Data Pin Questions

Post by Terrormaster »

adafruit_support_mike wrote:The datasheet doesn't have any specs for the current capacity of the output pins, but I doubt they'd be able to drive a solenoid directly. It would probably be a good idea to use the transistor or a mosfet.

Either way, you won't need a diode on the line that controls the transistor. The current path for the control signal will be independent of the current path through the solenoid.
Thanks. I've decided to go the transistor route for that very reason. My test circuit uses a single 6v across a TIP120 CE. The plan is to feed the DATA outputs into the Base of the TIP120 with a 1k resistor. Testing the circuit I'm feeding the same +6v back in to the base. I need to get a new battery for my volt meter (12v) so I haven't measured the actual output voltage going across the magnet. But so far the 1k drives the magnet pretty good without heating up the TIP120.

The thought is to use the same battery pack to drive the 1096 and the magnet. My concern now is if the current is significantly lower coming out of the 1096 the 1k resistor might be overkill and prevent the TIP120 from reaching saturation. The other thing I want to do is increase the source from 6v (4 AAA in series) to 9v (6 AAA in series) to increase the magnet strength. That's well within range of the 1096. But then the 1k might not be enough resulting in heating up the TIP120. Perhap the increase in voltage across the resistor will create enough of a compensation in current to account for lower current coming off the data pins. A delicate balancing act considering the output current of the data pins on the 1096 are an unknown at this point.

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Re: M4 Receiver - 315MHz 1096 Data Pin Questions

Post by adafruit_support_mike »

Don't worry about saturation.. the TIP120 is a Darlington, so the base current you send in gets beta-multiplied through one transistor and fed into the base of another. The nominal current gain is 1000, so 5mA is enough to saturate it with a 5A load.

Once you get your multimeter running again, take a current measurement through the coil. Divide that by about 300 and choose an input resistor that will deliver that much current when the voltage across it is Vout - 1.25v (the TIP120's operating input voltage). That will give you enough input current to keep the Darlington happy while not wasting too much power going into deep saturation.

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