I'm a newbie when it comes to this kind of stuff, but what I'm trying to do is construct a 0-10volt monitor that will light 20 less across the range to reflect the deviation of a saw blade in the cut, a different led depending on blade deflection. I have an analog 0-10 volt sensor but I need 20 less instead of the customary 10. I have a diy kit but it is set up for 0-20v. (schematic is available) I'm thinking its a simple matter of changing a couple of resistors in the kit, but I dont have the electronics background to figure it out. I would be grateful for any and all help
Kenneth

 

Welcome to the forum.

Do you mean LEDs?

Please post the schematic.

 

Please post a link to the DIY kit so we can take a peek. For my own curiosity, Is this a wood or metal cutting bandsaw? Are you using this to set the blade tension prior to operation, hence it doesn't remain on the saw?

 

This is the schematic that came with the kit.

 

The saw (sawing logs in a mill) on this peice of equipment is fed manually by an equipment operator. The problem is no matter how good he is the only way to tell if you are over feeding the saw blade is a pitch change in the sound of the saw or worse miscut lumber, worse case scenario--a damaged saw. I have a 200hz inductive prox sensor that can detect blade position change down to .004" with a linear 0-10v output. The goal is to translate this voltage change into a visible guide to the sawyer. LEDs in the middle lit, all is good, as the saw deviates from its correct position there will be a shift in which LEDs are lit (color coded green, yellow, red) to alert the sawyer he is pushing on the edge. Not only will this keep him from over feeding the blade it will let him know if he has a good cutting saw that can be pushed harder.

 

The problem is no matter how good he is the only way to tell if you are over feeding the saw blade is a pitch change in the sound of the saw...

That's a pretty good form of feedback, and one tuned to the process should be able to manage that. Would limiting drive torque not help? I've worked with a couple of planners/sawyers and they were very well tuned to sound/feel of thier equipment.

 

Sound is definately a good and usually reliable feedback signal but what I'm attemptIng is much faster. the indicators would respond with as little as 1/4" of log travel through the saw. There are on the market systems that do what I am attempting but they are cost prohi tone for a small albeit aggressive family own business: http://www.jacobson-engineering.com/bandmill.shtml, http://www.sawcontrol.com. see links for what is possible. The eventual goal would be to close the loop between feedspeed and saw deviation in realtime.

 

I don't understand the sentence," I have an analog 0-10 volt sensor but I need 20 less instead of the customary 10. Do you mean you need to convert the 10v analog signal to a 20v analog signal?

 

The diy kit has 20 Leds to indicate range of 0-20volts. I want the same 20 leds but indicating a 0-10 volt range. the chips in the kit are the national semi-conductor lm3914 which will equally devide the input signal across the leds if the resistors on some of the terminals are of "the right value"

 

http://www.national.com/ds.cgi/LM/LM3914.pdf

The above link will give you the datasheet with examples of how do do many different things with the LM3914. One is to make a centered display. That could be used to indicate Go Faster, or Slow Down in you application. It also explains how to calculate resistor values to give the range you need.

 

I guess this is where inexperience comes in I've looked at the datasheet several times and still can't figure out the resistor values that I need to make a 5 volt center with a 0-10 volt range.

 

After a closer look at the schematic you referenced for your kit, it looks like a 20K resistor placed between the lower end of the pot and ground should increase the sensitivity of your kit so it will work on 0 to 10V. Others may think differently and I encourage them to jump into the conversation.

 

Is there a chance that the onboard pot can change the range enough to get close to 10v? It makes sense that adding resistance below the pot will raise the signal voltage, making a lower voltage appear larger.

 

The documentation supplied is very limited in the form of information. It simply states that the range is selectable with onboard preset. The basic configuration would, at best, provide <=50% of the input. I couldn't determine whether the 0-20V spec means that it would, with moving the pot wiper toward ground, measure 0-100v. I would suggest, build it as shown and test. If it didn't provide the needed range, cut the ground trace for the pot and insert a resistor.

 

This is why I got this kit, adjustable pot, but after looking at it wasn't sure if it would work or if I just misunderstood the brief discription. I even tried to contact the manufacturer (info@eonkits.com) but no reply.

 

I know you've already purchased a kit, but another form of feedback to the operator would be a center-zero analog meter. The advantage of the meter is that it would likely only take a single resistor to calibrate it to work for you. Of course, it's perhaps not as easy to see in a dark room as LEDs, but it's something to consider.

 

I know you've already purchased a kit, but another form of feedback to the operator would be a center-zero analog meter.

You stole my thunder.
A center zero analog meter has great advantages in the eye fatigue department. Fact is, when DMMs started replacing VTVMs communication techs discovered quickly how irritating bobbling digits were when tuning
stages by peaking and dipping. It took a while before manufacturers added a bar graph to the display to make things easier.

On the other hand, LEDs will respond faster.

 

The LED display would not be a seven segment display but a row of color coded LEDs, green, yellow, red in line of sight between operator and saw blade. All he would need to notice is which LEDs were lit, similar to a bar graph but with the chips in dot mode rather than bar mode

 

My most favorite guitar tuner ever had a similar display; dot mode and a long row of LEDs. Visible from a distance and very easy to read precisely. I think this is a great approach if the OP can just get things scaled properly, which should be easy.

 

Would this work for what you need? http://www.national.com/mpf/LM/LM3916.html#Overview

data sheet http://www.national.com/ds/LM/LM3916.pdf

You would pick the led colors to suit the voltages. The input voltage could also be scaled to suit your needs.

Or this circuit could be expanded to as many levels as you want; http://www.aldinc.com/pdf/cd_23001.0.pdf