# Multi 555 chip controlling a single fuel injector

#### 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
13,234
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.

#### 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
3,905
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.

#### Luke Norman

Joined Jan 11, 2018
6
Ok, so I'm limited to one chip with a hall sensor for the trigger and one sensor for pwm variation .
Thanks

#### Alec_t

Joined Sep 17, 2013
13,234
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?

#### 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

#### 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
3,905
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
13,234
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.

#### 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
3,905
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.

#### WreckedSparky

Joined Dec 27, 2017
11
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.

#### Finjection

Joined Apr 18, 2020
3
I am trying to make for an old car an electronic injection system based on a 555 timer. I have several sensors including a map, how can I do?

#### Alec_t

Joined Sep 17, 2013
13,234
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?

#### Finjection

Joined Apr 18, 2020
3
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

#### Finjection

Joined Apr 18, 2020
3
I have already done several things, especially mechanics. with recovered pieces

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#### Jerry-Hat-Trick

Joined Aug 31, 2022
209
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 I'm 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.
Hi, I know this post is fairly old, but I really think it's still worth a reply. If I understand correctly you are looking at using a 555 monostable to fire the injectors. I really think you only need one 555 and the rest can be done with analogue circuitry. Assuming you are using a single injector in front of the throttle body you could put magnets around the crank pulley, one for each cylinder so that the the monostable fires each induction stroke. The only other sensor you absolutely need is a MAP (Manifold Absolute Pressure) because the mass of air drawn into each cylinder is almost proportional to the pressure so the monostable pulse duration needs to vary according to the manifold pressure. You are looking to achieve a stoichiometric air/fuel mixture by weight - about 14.7:1 for air/petrol. The exact timing is not so important - remember a carburettor pushes out fuel continuously. The difference between lean and rich mix is about 20% and for getting something working you can adjust the mix with a potentiometer. Important is to calibrate your injector by running it at varying mark space ratios into a measuring jar for a while. Typically, they take about 1.0ms to turn on and off after which they are fairly linear with time. More important is the fuel pressure - I recommend 4.0 bar - fuel injectors need fuel at a constant high pressure. You can use a higher pressure fuel pump with a pressure valve so fuel flows back to the tank when not needed, or there are now fuel pumps which don't need this return.

Most throttle bodies come with an inbuilt throttle sensor so you can use if you like - to squirt more petrol when you floor the throttle - although the manifold pressure goes up when you open the throttle so it's not essential. Processor driven EFI's are not as complex as everyone thinks. You could add other sensors over time but a dash mounted potentiometer to enrich/lean would probably suffice unless you are getting really sophisticated, in which case I'd recommend a processor, like the Seeeduino XIAO for example, as they are cheap and easier to use and adjusting variables is easier.

#### Jerry-Hat-Trick

Joined Aug 31, 2022
209
If You actually want an Engine that runs properly, get a Micro-Squirt ..........
https://www.diyautotune.com/shop/megasquirt-assembled/microsquirt/

It will cost You much less Money than trying to cobble one up from scratch.
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Thanks, I'm aware of this and other aftermarket ECU's. I found a Microsquirt ECU version 3.0 at $314. Cost of my electronics so far less than$15. More important, I'm interested to have a go and happy to spend the time to get it right. There is a lot of hype out there about the supposed complexity of ECUs - the original Megasquirt worked happily with an 8 bit Motorola processor. I'm sure you intended no offense when you suggested I'm "trying to cobble one up"