Multi 555 chip controlling a single fuel injector

Thread Starter

Luke Norman

Joined Jan 11, 2018
6
I know that a single 555 chip can be used to control a fuel injector with inputs from a hall sensor and a pot to act as a simple fuel injection controller to run an engine. But what im wondering is if it is possible to use multiple chips so that they can feed the one another so that more sensors could be used ? Say one 555 with a pot as a throttle position, a hall sensor for a trigger, then feeding into another 555 with a temp sensor, then that 555 feeding into a 3rd 555 with a barometer? I know it would be a pain to tune, but would it work? Sorry if this simple, I'm new to using ic chips.
 

Alec_t

Joined Sep 17, 2013
12,900
Welcome to AAC!
I can't quite follow what you are trying to do, but it is certainly possible to use the output of one 555 to trigger the input of another 555.
 

Thread Starter

Luke Norman

Joined Jan 11, 2018
6
So a single 555 can control an engines fuel by using a hall sensor to act as a trigger and a pot or map sensor to create a variable pwm output based on the engine load to fire the injector. Essentially creating a simple fuel injection system with the 555 acting as the ecu. Now if we took say 3 555 chips, and had the first was set up the same as above, would it be possible for the first chip to feed a second chip with another added sensor, such as a barometer, so that any atmospheric pressure would also alter the pwm signal, with a 3rd chip fed from the second chip with say an air intake temp sensor, so that as that value changes it would change the over all pwm signal comming from the 3rd chip that is controlling the injector. Essentially can extra chips be added in series so that multiple sensors can impact the final pwm output?
 

LesJones

Joined Jan 8, 2017
3,749
No. A PWM signal can only contain information about one thing. It is not like a CAN bus which can carry information from many sensors. A CAN bus sends information digitally. PWM is more like an analogue signal. The ratio of ON time to OFF time (called the duty cycle) is what represents the value of the signal. So if the signal was low for 50% of the time and high for 50% of the time it represents half of the maximum value of the signal. The frequency of a PWM signal does not change for a particular system. (Not all systems use the same frequency.) A PWM signal can be converted to an analogue voltage by passing it through a low pass filter.

Les.
 

Alec_t

Joined Sep 17, 2013
12,900
Now that I've a better understanding of your project, I think the outputs of the MAP sensor/pot, pressure sensor and temp sensor could be conditioned and combined in an op-amp to produce a sum signal which controls the duty cycle of a single 555 to give the PWM signal for driving the injector. Would you need a second 555 to provide an advance/retard delay between the Hall sensor output and the first 555 trigger input?
 

Thread Starter

Luke Norman

Joined Jan 11, 2018
6
Now that I've a better understanding of your project, I think the outputs of the MAP sensor/pot, pressure sensor and temp sensor could be conditioned and combined in an op-amp to produce a sum signal which controls the duty cycle of a single 555 to give the PWM signal for driving the injector. Would you need a second 555 to provide an advance/retard delay between the Hall sensor output and the first 555 trigger input?
That could work, essentially I was wondering how to add more sensors(which output 0-5v) to variate the pwm of a 555 chip, as with the single chip variation, the pot(or map sensor, both have been used with success) to increase or decrease the pwm to the injector. With the single chip set up, the trigger essentially acts as a reset, so for each revolution of the engine, the pot defines the amount of fuel the injector dispenses with pwm. As engine load increases, if the rpm stays the same , the pot/map(in correlation to the amount of throttle applied) will increase the pwm output to the injector, injecting more fuel. So would maybe the hall sensor on the final 555 chip work if the final chip was sending out the pwm, and the other chips where just creating variances that altered the final pwm output? Sorry for all the questions, this is all 100% new to me , I can figure out programing and make microcontrollers function together, but am new to the basics of electronics and timer chips and ic's
 

Thread Starter

Luke Norman

Joined Jan 11, 2018
6
****Edit.
Just re-read your post. If all the sensors could be combined/conditioned into one input, would an op amp provide a reliable outout signal that would vary a minute amount given the inputs of the other sensors? Essentially, this would reduce the amount of time tuning the system with variances in weather and elevation. I tried to edit the previous post but exceeded the time limit to edit it
 

LesJones

Joined Jan 8, 2017
3,749
I had missunderstood what you were trying to do. I thought you were trying to combine data from several different sensors into one PWM signal to feed to an ECM module or some kind of display. Now that Alec seems to have worked out what you are trying to do I think I understsand. This is now my understanding of what you wanted to do. You wanted the length of time the injector was open to be the sum of a number of lengths of time each of which was controlled by the reading from a sensor. Is my understanding correct ? I have never been involved in the design of fuel injection systems but I think the calculation of the injector opening time is much more complicated than just adding values together.

Les.
 

Alec_t

Joined Sep 17, 2013
12,900
I think the calculation of the injector opening time is much more complicated than just adding values together.
Agreed. That's where the individual signal-conditioning comes in, prior to summing. I would expect the raw sensor signals to require some sort of non-linear scaling and an offset perhaps.
 

Thread Starter

Luke Norman

Joined Jan 11, 2018
6
Agreed. That's where the individual signal-conditioning comes in, prior to summing. I would expect the raw sensor signals to require some sort of non-linear scaling and an offset perhaps.
I was thinking if they become a combined signal I could have a pot in conjunction with each of the sensors for fine tuning each of the sensors. Once they are dialed in, they shouldn't need to be adjusted. It would take a bit of tuning but I think it would work once it's dialed in? It would essentially be an analog fuel injection, and pots would be the tuning method, vs modern ECU's that are tuned through software. I know that I could do an Arduino ecu and tune with software, but I'd like to try something different.
 

LesJones

Joined Jan 8, 2017
3,749
If you know how to write the software to make an Arduino function as an ECU then you must know how complex the calculations are that it has to do. I would not know where to start with such a project. I think you would need at least to use op amps to generate non linear functions. So you would basically be building an analogue computer ECM.

Les.
 
To understand what you're trying to accomplish, you want a controller that varies a spray of said fuel (I'm guessing methanol) based off pressure, RPM, throttle input and charge temps? An increase in one variable would increase the output of the injector? I know you could buy a Torqbyte controller or Arduino, but what's the fun in that.
 

Alec_t

Joined Sep 17, 2013
12,900
Welcome to AAC!
I suggest you read all the above posts carefully so that you realise how challenging this would be. The 555 is not the problem: the problem is all the signal conditioning that would be necessary. Are you up to building what amounts to an analogue computer?
Would your car modification be street legal and approved by your insurer?
 
Thank you for answering, I did not think that after 1 year someone would. My English is not good so I apologize in advance.
if I want to make an analog ecu. and don't worry about insurance in Cuba it is not necessary
 
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