Comparator Help Please
Comparator Help Please
(OP)
Hi,
I'm trying to design a simple delay circuit for a Peizo Electric buzzer to be used on a 24 VDC vehicle, I bought 30 of these LM211-N Comparators thinking they would be up to the task.
On the data sheet it says the output is good for 50 mA but I don't seem to be able to get it to pull up more than 0.06 mA,
It won't pull down from the positive rail at all what am I doing wrong?
I also want to be able to get the delay to around 2 seconds, my RC theory is all gone, cam someone tell me what value of resistor to use with a 1 microfarad capacitor.
I figure the input impedance of the LM211 is very high
Sorry, having trouble getting the sketch on here.
Thanks a lot
Roy
I'm trying to design a simple delay circuit for a Peizo Electric buzzer to be used on a 24 VDC vehicle, I bought 30 of these LM211-N Comparators thinking they would be up to the task.
On the data sheet it says the output is good for 50 mA but I don't seem to be able to get it to pull up more than 0.06 mA,
It won't pull down from the positive rail at all what am I doing wrong?
I also want to be able to get the delay to around 2 seconds, my RC theory is all gone, cam someone tell me what value of resistor to use with a 1 microfarad capacitor.
I figure the input impedance of the LM211 is very high
Sorry, having trouble getting the sketch on here.
Thanks a lot
Roy
RE: Comparator Help Please
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Comparator Help Please
RE: Comparator Help Please
Ok,
Here is the file, amazing what you can do if you read the instructions eh!
I show it on ± 15 Volts, that's my breadboard supply but I need it to work on a single sided 24 VDC, (24 Volt vehicle)
RE: Comparator Help Please
http://www.onsemi.com/pub_link/Collateral/LM211-D....
Connect the buzzer between the output and the + supply VCC, like RsubL.
You have to connect pin 1 and pin4 to ground.
Mike Halloran
Pembroke Pines, FL, USA
RE: Comparator Help Please
There's the problem, I don't have a ground, is it the same to tie 1 & 4 to - 10 which will end up chassis?
I have marked up the sketch to show how I intend to wire it to the machine
Is this how it should be wired?
Not I have added the front end, you can see it goes from around zero to near 24 Volts when the Proximity switch turns On.
RE: Comparator Help Please
Mike Halloran
Pembroke Pines, FL, USA
RE: Comparator Help Please
What size resistor would I need for the 1 µF to charge to 16 Volts in ~2 seconds
I assume the comparator input is high enough impedance not to interfere with charging
The specs say
Input Offset Current 10 nA
Input Bias Current 100 nA
I assume I may have to switch the inputs to get it to switch the buzzer on after the Proximity switch closes.
I was a bit confused by capacitors, I thought originally of using something like a 100 microfarad electrolytic, Digikey don't list electrolytic type only Aluminium, is that the same thing, I ended up getting Ceramic.
RE: Comparator Help Please
DigiKey sells Aluminum Electrolytic capacitors. You'll want one rated for twice the voltage you plan to use it at.
Z
RE: Comparator Help Please
I take it C is in Farads
So I have 1µF ceramic capacitor charging through a 100k resistor
1
------------------ shouldn't that be a time constant of 10 seconds?
0.000,001 * 100,000
With the negative input set half way between the rails I don't see any time delay when I switch the resistor feeding capacitor from negative to positive.
What am I doing wrong?
Thanks
Roy
RE: Comparator Help Please
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Comparator Help Please
Math is not my strong point
the 1 / (0.000001 x 100,000) gave me 10
So I need 100microfarad or 10Megohms for 10 Seconds
Thanks
Roy
Never mind, I just found the right formula on Wikipedia
RC Time Constant T = RC
RE: Comparator Help Please
I can fine tune it with a trimpot on the negative input
Thanks for the help
Roy
RE: Comparator Help Please
Z
RE: Comparator Help Please
What's a Gerber File and is there an easy way, think cheap, to generate one.
I started to make my own circuit boards using the iron on etch resist. I soon realized I need professional help.
There is a company here who can turn them around in 24 Hours with a file.
Thanks
Roy
Never mind, I found this explanation
http://circuitpeople.com/Blog/WhatIsAGerberFile.as...
I wonder if this old dog can be taught another new trick
RE: Comparator Help Please
You normally use a "layout tool" to pictorially describe/draw/create your board's traces, holes, thru-holes, and pads.
Normally you use "schematic capture" software to draw the schematic on which each part is described electrically, part number wise, and package type.
The output of the schematic capture is used by the layout tool to assign each physical component and to "rat's nest" how the components are all interconnected.
The board designer interactively "places" all the parts using the apparent physical aspects, knowledge of routing issues, required physical constraints, and good electrical layout rules to "route" the board using agreed upon "design rules". Design rules describe "via holes" (thru the board inter-connects), board thickness, trace widths, trace thickness, and allowed minimum spacing between adjacent traces called "clearances".
Once the board is laid-out and approved by the person requesting it a "Gerber conversion" is done which is usually an automated procedure using the converter to produce the Gerber files.
The Gerber files describe the various aspects of the circuit board in layers. Typical layers are: solder side, component side, silk screen, solder mask, and drill layer. These "layers" are used by "light plotters" that paint photons on "resist" a chemical coating put on the raw "copper clad" material of physical board. When exposed to light the resist prevents the dissolving-off of the copper cladding in the board etching process - which leaves the traces on the copper-clad. The drill layer and a text description explains where and how big to drill the board's holes. The boards are then "isolated" from the matrix they're usually made in.
Asking for a one day layout is often suicide for the process - especially if this is your first time. It will also cost you perhaps 20X more than a normally paced process.
If you just need a simple 15 parts or less board you can sometimes draw it in a cad package as only islands-of-copper by drawing only lines of isolation. Then using "mechanical etching" by which is meant a CNC router, you cut off the copper to isolate the copper islands that make up your circuitry. Then you drill the needed holes and hand assemble your bonified circuit board.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Comparator Help Please
Caveat: I've never used any of these, and at least a couple of them appear to be quite manual intensive.
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Comparator Help Please
I just hope the board manufacturer can write these for me otherwise I'll be back to the Laser printer and transfer paper.