Seeking help on circuit design for LED rudder indicator

[weegiemann]

Hello,

I have just joined the forum as I am looking for help in designing a circuit that I can use as a rudder indicator. Basically I am looking to have a row of red and green LED's light up sequentially when the rudder is moved in one direction or the other , typically 8 LED's in each direction. I would be looking to drive it from a wire wound pot connected to the rudder or any other method that would provide a reliable robust sender.

does anyone have any circuits out there or can point me in the right direction, I used to do hobby electronics in my younger days and can etch boards and have good soldering skills, Programmable chips are currently not something I have any experience with but open to learning new skills.

thanks for any assistance coming my way

Weegiemann

 

[Alec_t]

Welcome to EP!
If you're happy with 5 LEDs in each direction then an LM3914 and a pot, plus a few bits, are about all you need.

 

[weegiemann]

Alec T,

tks for the reply, you wouldnt happen to have a circuit diagram I could follow would you ? , 5 x LEDs each side are good enough for my purposes.

How stable would it be once it was set up and would I be able to configure it with an electronic zero facility in order to maintain it reading zero when the rudder was amidships.

 

[weegiemann]

Alec T,

I have looked at some LM 3914 circuits on google and from what I can see it can only have the LEDs lighting up sequentially which would not give me the capability of splitting them into 2 x banks of 5 so that when the rudder is in the middle no LEDS are lit but when it goes to one side ie right side ( green) the LEDs start to come on sequentially the further over the rudder moves , When I bring the rudder back to the middle they go out and when I move the rudder to the left the red ones come on in the same manner.

 

[weegiemann]

Alect,

Tks again I managed to find a circuit that I will be able to use .

Do you have any comments or recommendations that I should incorporate into the design.

It will be powered by 24 volt and I was thinking that to maintain a stable ouput I should be looking for a voltage dropper to from 24v to 5 volt.

I will use a wire wound pot fitted into a oil filled housing to ensure that it does not get adversely affected by corrosion.

 

[Alec_t]

Nice find. I've simulated that circuit on a 5V supply and it's fine.
For a ~10mA LED current make R1=R1'=R2=1k2, and R2'=3k9.
22k is a standard value for the pull-up resistor from pin 11 of the first LM3914.

 

[weegiemann]

Alec T,

thanks again for pointing me in the right direction with the LM 3914, I've ordered all the components along with a breadboard. Hopefully soon have it up and working and in place. I think I may have to use a bigger value pot as I only have an included angle of about 100 degrees on the rudder, that or use some plastic gears. It is getting more interesting as I get into it.

 

[Alec_t]

The posted circuit assumes the pot has end-to-end travel. If travel is only 100 degrees (presumably 50 left and 50 right) you could avoid the need for gears by changing some of the fixed resistor values. A different pot wouldn't really help. I'll re-run the sim and see if I can come up with a suggested mod.

 

[weegiemann]

Alec T ,

Once again tks for yoru help, if I can avoid the need for gears it makes the interface to the rudder shaft so much easier.

 

[Alec_t]

This mod should do the trick (only the relevant circuit part is shown).

For the simulation I've assumed the rudder pot travel is 50 degrees either side of centre and that the pot resistance track end-to-end extends over 240 degrees (your mileage may vary). A couple of trimmers allow for adjustment to set the RLo and Rhi limits of the LM3914s. The rudder pot resistance isn't critical. If you're going for a wirewound one your choice may be limited. Higher resistance = less robust but not so current-hungry.

Edit:
The rudder pot should connect between +5V and ground.

 

[weegiemann]

AlecT,

Good day to you,

got my circuit up and running however on reflection it would be better if I had a bar display which would light up instead of a single LED light on to denote port or starboard rudder. The current circuit lends itself well to a single pot ie midpoint on pot is midpoint on rudder and left or right denotes port or starboard rudder and the LED light in dot mode lights accordingly.

I am trying to think around this but I can only see it working with a 2 gang pot running 2 seperate LM 3914's, can you offer any advice here or do you have a 'cunning circuit' that would operate it from one pot so that I could get a bar display to show port or startboard

 

[duke37]

Pin 9 controls single led or bar.

 

[Alec_t]

As Duke says. Connect both pins 9 directly to +5V. Remove the link from U1 pin 9 to U2 pin 1.
Like this :-

This will give you a single bar display, starting at one LED and progressing to 20, but I'm not sure if that is quite what you're after?

 

[weegiemann]

AlecT & Duke37,

Tks for your responses but that is not what I am looking to achieve, what I need is a zero center bar array , I think I have found what I am looking for in this circuit, I will have to wait until I get the LM 337 and then experiment a bit with it until I get it to work . If either of you have any comments or advice on this circuit to give me I would appreciate it.I dont quite understand it so far, ie where does the LM337 get powered from and where do I get the input signal from ?? Thanks for all your time and help so far.

 

[Alec_t]

what I need is a zero center bar array

Can you post a sketch of that display?

Edit:
Your post #14 circuit will give the same visual display appearance as the post #13 circuit. The only difference is a 1.3V offset in the signal voltage needed to drive the display.

 

[weegiemann]

Can you post a sketch of that display?

Edit:
Your post #14 circuit will give the same visual display appearance as the post #13 circuit. The only difference is a 1.3V offset in the signal voltage needed to drive the didplay.

AlexT,
I have attached a blk diagram showing what I am trying to achieve. Basically I want a series of green leds to light up in bar mode when the rudder is to the right of the centre position , ie further to the right the rudder goes the more leds light up to give an indication of angle and then when it is brought back to the centre position the leds go out according to the angle of the rudder as it approaches the zero position. As the rudder moves to the left the green (right) leds would remain off and the red (left) leds would start to light up in the same manner ie the greater the angle from the centre position the more leds would light ( ie bar mode). Ideally in the centre position no leds would light up but this might be too much messing around. I was thinking of using 2 x LM3914s to drive 2 seperate displays, ie one for the right and one from the left and have a 2 gang pot connected to the rudder with each LM3914 being driven by its own pot. This would be a simple way to do it but I was wondering if I could get it to work from one pot .

 

[Alec_t]

That's now clear. The green (starboard) LED driver will work in the conventional way, but the red (port) LEDs will require an inversion of the logic. The post #14 circuit can't do that, even with use of a 2-gang pot. Seems to me there are three approaches; either add inverter stages for each port LED, or jiggle with the way the port 3914 reference voltages are generated, or use an opamp to invert and offset the driving signal voltage for the port 3914. I'll have a play and see if I can come up with something.

 

[Sunnysky]

wouldn't U rather have a servo controller to set the rudder position like those used in RC hobbies.

 

[Alec_t]

Now that you've opted for a bar display, power dissipation in the 3914 chips becomes an issue. The recommendation to reduce heating is to include a series resistor between the positive supply and the rail to which the LED anodes are connected. For a 12V supply and 10mA LED current a 2W resistor of about 100 Ohms would do. For a 5V supply and 10mA LED current a 22 Ohm 1W resistor would suit. A 10uF capacitor between that rail and ground would provide supply decoupling.

 

[Sunnysky]

Now that you've opted for a bar display, power dissipation in the 3914 chips becomes an issue. The recommendation to reduce heating is to include a series resistor between the positive supply and the rail to which the LED anodes are connected. For a 12V supply and 10mA LED current a 2W resistor of about 100 Ohms would do. For a 5V supply and 10mA LED current a 22 Ohm 1W resistor would suit. A 10uF capacitor between that rail and ground would provide supply decoupling.

close... mult both R suggestions x10