Help creating a circuit

[thomas188]

Hello, and thanks for the help in advance.

Here's what I'm wanting to do.

I have a sensor that throws out values 0-100 in .2V increments. (Throttle Position Sensor). When the TPS is at 100% the sensor will send out 5v. I need to turn on another system when the TPS is at 100% (5v), and only during this time +/- 5%.

What kind of switch,relay, module would be voltage operated? How can I build a system to monitor the voltage and when it reaches 5v, send a signal to a relay that will then turn on another operation?

 

[Grossel]

What is your input? You must explain your TPS, else it's hopeless to give any sensible answer.

 

[LTX71CM]

Is this for a NOS system or other performance enhancer? As is commonly done just use a microswitch that's closed with the throttle is at wide open. You can do this under the hood or by the pedal. Just be careful to mount your switch in a way that won't snag pedal or cable which would cause undesired acceleration. Safety first.

 

[Neal]

comparator

 

[thomas188]

As far as the input to the TPS, I'm confused, sorry. ASAIK it is 12v in and 0-5v out to the PCM.

This is for a NOS System, but it is going on a motorcycle and there is no room as the throttle blade is in-between the throttle bodies (< .675" space)

 

[thomas188]

Is this any help?

 

[picbits]

Normally you'll find you have 3 terminals on your throttle position sensor. These are +5v, ground and output which varies between 0 and 5 volts depending on where the throttle actually is (unless its something silly like a PWM throttle sensor).

As above - you can use a simple comparator or a window comparator for this purpose (you can get loads of info from a quick Google of it).

 

[Reloadron]

The throttle position sensor in most cases (not all systems) is a potentiometer that outputs 0 to about 5 volts, however that can vary as can be seen here.

Idle can be between 0.6 and 0.9 volts while wide open throttle can be between 3.5 to 4.7 volts. The attached circuit is a hack job from another comparator circuit that I had. I made the zener diode 4.7 volts so the outputs will toggle at about 4.7 volts. You may even want a 4.5 volt zener in there. The output of U1A pin 1 could drive a small NPN transistor like a 2N3904 or 2N2222 which could drive a small relay. Use a transistor base resistor around 4.7 K Ohm. Anyway, something like this could work. This is just a basic hacked circuit attached suggesting the use of a comparator. If you want to go this route a circuit could be put together using a single comparator. The thing would be about the size of a book of matches give or take.

What needs to be known is the exact voltage out of the TPS at wide open throttle.

Ron

 

[MikeMl]

Previous thread on almost the same topic.

 

[thomas188]

I just looked in the manual and it calls for input voltage of 4.5-5.5v at WOT the voltage should be ( (Input voltage x 0.824) w/in %10)

so.... 3.33v~4.08v should be Vo at WOT

So if I build it to look for voltage>3.33 then it will be at a minimum of %90 throttle which I can set the tuning software to start being rich at 85% throttle to be safe

 

[thomas188]

Ok, I worked on this subject for a few days. I understand how the comparator works now. I can get a 1v out when I put the Vcc at 12v with a ground and then v- at 12v and v+ at 5v..

The TPS output is at 4.53v at WOT with a 5.01V input.
The LM339N says it has 50ma draw

I connected a 15ohm resistor between the TPS input (5v) and the v+ and the voltage drop was neglible did I do something wrong? 15*.05 =.75v drop so i should be seeing ~4.26v shouldn't I? I notice the zener diode in the diagram, how is that made, how could I make one to be around the 4.2-4.35 range?

Also, is the 1v digital output from the LM339 stront enough to trigger a relay?

 

[MikeMl]

Did you wire it up as I showed in this schmatic? From the questions you are asking, I'm guessing you didn't.

If not, post how you wired it?

 

[reidinstruments]

Hello, your circuit that you want is very simple and be done very cheap and easy using a microcontroller. If you want one built for you so you just plug and play let me know and I can make one for you or tell you what you need. I am an electronics engineer and I build and design small prototypes for companies and individuals. Just to give you an idea, the size of the unit could be less than 2" x 2" and would cost around 10 bucks to make yourself. If you want one built to youre exact specs it would prob cost around $35.00.

 

[thomas188]

I have submitted a picture. I am new to this so I don't fully understand all of the schematic, and I didn't see this schematic earlier either. I saw another one with a 4.7 zener diode, I understood that schematic much easier, but I need around a 4.2 zener diode and I'm rough on understanding how they work. Look at what I did and see where you can offer advice.

Thanks much!

 

[MikeMl]

Your circuit is much too simplistic. The LM339 requires many external components to make it work for your intended purpose. The circuit I posted is about the minimum parts count that will pull-in a small relay when the TPS voltage is greater than what the pot is set to (the trip point is adjustable using the pot) I use an 8.2V Zener to create a reference voltage that doesn't vary with engine speed, also to protect the circuitry from transient voltage spikes that may exist in the car's electrical system.

 

[thomas188]

I have attached a scan of the schematic you provided Mike. Can you look at it for me please.

Thanks for all the help. I truly am new to this, engineering physics was pretty much just basics and it was tough at the time

 

[MikeMl]

Physicists have trouble operating a scanner, too

 

[thomas188]

LOL...enough said.

 

[MikeMl]

Before I answer your questions, what load will this circuit be switching?


If you need a relay to switch that load, what is the coil resistance and voltage rating of the relay you are going to use?

 

[thomas188]

There is not a coil resistance on the box for the relay I purchased, I can check with the meter when I get off work. It is a 30a 5 pole 12v relay though