multiple inputs into a 555 timer to control servo

[mturner642]

i am trying to control a servo using a 555 timer circuit. i have already designed my timing circuit and have been successful with just signal input to the timer. now i am having problems trying to connect 3 seperate signals into my timer. I am receiving my signals through 3 inductive sensors. The signal goes through my comparator and then checked once again by an AND gate. I have it connected so that each output of the and gate is connected to a single wire running to the timer. I am using 3 different pots to provide 3 different signals to cause the servo to adjust it's angle. When i hook it up in this manner, the servo acts as if there is no signal being sent to the timer.... does anyone know why or perhaps offer any tips?

Thanks,

Marc

 

[AllVol]

i am trying to control a servo using a 555 timer circuit. i have already designed my timing circuit and have been successful with just signal input to the timer. now i am having problems trying to connect 3 seperate signals into my timer. I am receiving my signals through 3 inductive sensors. The signal goes through my comparator and then checked once again by an AND gate. I have it connected so that each output of the and gate is connected to a single wire running to the timer. I am using 3 different pots to provide 3 different signals to cause the servo to adjust it's angle. When i hook it up in this manner, the servo acts as if there is no signal being sent to the timer.... does anyone know why or perhaps offer any tips?

Thanks,

Marc

It's hard to say from just your description -- a circuit diagram would be helpful, if possible.

Off hand, I would say you are trying to trigger the 555 with a positive (logic high) signal on pin 2, but it must be a logic low (0) to cause the timer to fire.

Also, you can combine inputs all you want, but I hope you realize you will get only one output from the 555, that which it is set up for.

Perhaps you might also explain what you expect the servo to do when it receives a signal.

 

[Boncuk]

Servos for R/C control work at variable pulse lengths of 1.0 to 2.0ms at a PRT (pulse repetition time) of 20ms. 1.0 and 2.0ms pulse lengths are for full deflection L/H and R/H. The center position requires exactly 1.5ms.

Wire the 555 as an astable MVV the way it generates the variable pulse lengths using a pot. (Longer or shorter pulses will be ignored, meaning you won't have the entire mechanical way of the pot for fine tuning.) The duty cycle should be 10% and the frequency is of minor importance.

Boncuk

 

[mturner642]

i understand that the 555 timer will only react to what my input voltage to the 555 is. What i am hoping to achieve is that depending on which sensor is activated, the corresponding voltage will activate the timer and make it adjust to a position that i want. My project is to control a elevator, like that on a airplane, and cause it to move depending on which sensor is activated. So far i am having zero luck using 3 seperate voltage signals. My 555 control circuit is made up of 2 555 timers. the first timer creating my pulse and outputing that pulse signal to my second timer that is the controller for the servo... Am i better off just using a single 555 timer? I am new to controlling servos and appreciate any help.

Marc

 

[Boncuk]

Hi mturner642,

why don't you just switch different resistors into the circuit? Applying voltages to any input other than contained in a timer circuit you'll mess up the timer IC.

So instead of switching different voltages you might switch different resistors.

Have a look at the example. It does not match your requirements concerning timing.

Boncuk

 

[mturner642]

Is it possible to use 3 555 timers? Each 555 timer is setup to create a different PW, just you just described Boncuk. I guess my understanding of just how a 555 timer works was off. I thought that i could feed different voltages into a single 555, but perhaps i should just feed each of them the same voltage, but instead design each 555 circuit to create a different PW. I am using a Futaba servo, like those used on RC planes. They do not provide a lot of information on requirements for the servo.

I really appreciate all your help!

Marc

 

[mturner642]

could someone show me a valide astable circuit that i could use? i've been coming the internet and haven't been able to find a circuit that sounds useful. everyone does it differently and it's becoming difficult to determine just which one works.

 

[Mikebits]

I found this servo tester circuit on the web. You could combine the two 555 chips into a single 556 dual timer. The pot controls the pulse width. Perhaps you can have your 3 input voltages control an analog switch and switch in 1 of 3 resistor values.