Looking for electronic switching device ideas

[Dr.Jeff]

One diode should suffice.

Thanks Brian, good to know. For the switching controller, I'll look closer at Rachael's video reference and see if I can figure out a way to make one. But I'd still prefer to find something premade.

Appreciate all the input from everyone.

 

[Russe11]

...Honestly I will not be cranking anything by hand for several hours. ...

I must have missed that design criteria.

Here's another purely mechanical switching idea: many electric motors are nominally 1800RPM. 1800RPM = 30Rev/Sec. You could couple a motor to a rotary switch. Or put a cam on it that actuates a momentary switch.

I'm just throwing ideas out there, not advocating them as a better route. Just trying to give options that fit the skill set you've described.
Good luck & have fun.

 

[Dr.Jeff]

Here's another purely mechanical switching idea

That's certainly doable, thanks for the idea. Wouldn't require much of a motor so a faster smaller one might be found. If nothing turns up on the 'electronic' side then I'll consider it.

 

[Dr.Jeff]

The video Rachael posted shows a great design because it is completely adjustable. The only image of the circuit that I could see is the one she posted, a screen shot from the video:

Unfortunately it does not give me enough information to see if there is any way I could try and replicate it. And the dialog in the video doesn't offer much more info. Not sure if anyone can gain enough from it to offer more detail? I searched the source of the video to see if I could find more about the design. The company sells complete units for around $500, or they will sell a DIY kit to make one - but honestly is it still way more than I want to spend for this limited application. What's funny is in the video he states the components involved are less than a couple dollars worth, but then they sell the kit for a lot.

However when searching for that video I found a couple more systems that are similar. Both are home built units with the same basic architecture, but different approaches. Here are images I got from them, perhaps it is enough to come up with something.

The first one is extremely simple and I do not think it will hold up. He is driving one injector directly from the 555 chip, so it would need some sort of relay/MOSFET added. And I don't see any of the protective bits on it. I like the fact it has a potentiometer to adjust the speed, but according to his description the fastest speed is still much less than I'd like. Perhaps some of the components (resistors, capacitors, not sure what) could be changed to increase the speed range? Here is the schematic:

Based on what little I understand, I think this needs some improvements.

The other one I found went through a couple revisions. It started with this basic idea, using the 555 chip in a "astable" layout to control the injector pulses. Although the design is very similar to the one above, it is different. For one thing all 8 legs of the 555 chip are not used like they are on the one above. Also is has completely different values for most of the components. But I have no idea what any of the difference mean:

Then he added another 555 circuit in a "monostable" layout to limit the amount of time the first circuit runs. I would not need that second portion of it, but he also added several other improvements elsewhere to make the circuit more stable. NOTE: there was another version before this that did not include some of the additional components, which he states were added to improve the overall design (but he did not state what the 'improvements' were for). I was not able to get an image of that simpler version:

Similar to the first one I noted (with the adjustment feature), this design is still too slow. But he noted that changing resistors R5 and R6 plus capacitor C7 will change the speed that it cycles at. Unfortunately there was no info about what to change the values to. Otherwise it appears to be more advanced than the first one.

I'm wondering if the best elements of all of these can be used to make a simple version that cycles fast enough, perhaps has some adjustability, but without the unneeded stuff?

Honestly a lot of what I've said here is just repeating things from the web pages, and I do not fully understand everything. I follow the general principles, but not sure if I could actually build one. But I'd be willing to give it a try if someone assists with the parts list and possibly some tips on how to do it.
Thanks.

 

[Dr.Jeff]

Not to get too far off from my last post, but I also have a different question about all this.

Previously a couple of you have mentioned using a PWM controller to cycle the injectors. If I understood correctly the issue is they might be too fast, with some mods possibly needed to slow it down. Mention was made of the unit's frequency rate. This reminded me of another recent question I had about using a PWM controller for the heater/AC blower motor. In that discussion a PWM with a higher freq was preferred to help eliminate noise. But I'm guessing in the current application noise isn't an issue, so finding the lowest freq would be preferred? That would offer a bit slower speed?

Also, how does the variable rheostat potentiometer thingy act in this respect? I'm guessing the freq of the PWM is the fastest it cycles with the knob cranked up to 11 (remember that reference?), and turning the knob toward zero will slow it from there? So will it need any circuitry mods, or just a turn of the dial to get it to about the right speed?

I ask because I recall the inexpensive PWM devices were built on the same 555 chip thing as those circuits shown in my last post. So they might be pretty much exactly what those circuits are building? If that's the case then I'd rather buy one of those cheap PWM's than try and build my own.

I know this is likely another of my over thinking exercises, but that's how I learn about new things. And I enjoy it, so if anyone is willing to play along and help me learn I appreciate the education.

 

[dllubin]

The video Rachael posted shows a great design because it is completely adjustable. The only image of the circuit that I could see is the one she posted, a screen shot from the video:

Unfortunately it does not give me enough information to see if there is any way I could try and replicate it. And the dialog in the video doesn't offer much more info. Not sure if anyone can gain enough from it to offer more detail? I searched the source of the video to see if I could find more about the design. The company sells complete units for around $500, or they will sell a DIY kit to make one - but honestly is it still way more than I want to spend for this limited application. What's funny is in the video he states the components involved are less than a couple dollars worth, but then they sell the kit for a lot.

However when searching for that video I found a couple more systems that are similar. Both are home built units with the same basic architecture, but different approaches. Here are images I got from them, perhaps it is enough to come up with something.

The first one is extremely simple and I do not think it will hold up. He is driving one injector directly from the 555 chip, so it would need some sort of relay/MOSFET added. And I don't see any of the protective bits on it. I like the fact it has a potentiometer to adjust the speed, but according to his description the fastest speed is still much less than I'd like. Perhaps some of the components (resistors, capacitors, not sure what) could be changed to increase the speed range? Here is the schematic:

Based on what little I understand, I think this needs some improvements.

The other one I found went through a couple revisions. It started with this basic idea, using the 555 chip in a "astable" layout to control the injector pulses. Although the design is very similar to the one above, it is different. For one thing all 8 legs of the 555 chip are not used like they are on the one above. Also is has completely different values for most of the components. But I have no idea what any of the difference mean:

Then he added another 555 circuit in a "stable" layout to limit the amount of time the first circuit runs. I would not need that second portion of it, but he also added several other improvements elsewhere to make the circuit more stable. NOTE: there was another version before this that did not include some of the additional components, which he states were added to improve the overall design (but he did not state what the 'improvements' were for). I was not able to get an image of that simpler version:

Similar to the first one I noted (with the adjustment feature), this design is still too slow. But he noted that changing resistors R5 and R6 plus capacitor C7 will change the speed that it cycles at. Unfortunately there was no info about what to change the values to. Otherwise it appears to be more advanced than the first one.

I'm wondering if the best elements of all of these can be used to make a simple version that cycles fast enough, perhaps has some adjustability, but without the unneeded stuff?

Honestly a lot of what I've said here is just repeating things from the web pages, and I do not fully understand everything. I follow the general principles, but not sure if I could actually build one. But I'd be willing to give it a try if someone assists with the parts list and possibly some tips on how to do it.
Thanks.

Dr Jeff:

I'm not sure what the speed issue is about. The 555 can operate in the microsecond range. Both astable and monostable speeds are determined by the externally adjustable time constants. That is what most of the resistors and capacitors (except the power supply bypassing ones) are for. You could certainly make it way more than fast enough for the speeds you were talking about. If you find one of those circuits suiting your needs, you can easily adjust the resistor and capacitor values. The 555 has been around for a really long time and the data sheet has a real good explanation of what it does and how it works that does not require an electrical engineering degree to understand. I recommend checking out sections 1,2,3, and 7 of the TI data sheet at http://www.ti.com/lit/ds/symlink/lm555.pdf and all will become clear. Don't worry about the tables full of numbers and graphs just yet.

 

[Dr.Jeff]

speeds are determined by the externally adjustable time constants. That is what most of the resistors and capacitors (except the power supply bypassing ones) are for

Thanks. That was my understanding, however I have no idea how to determine the correct values to use for those resistors and capacitors, nor where each one would fit into the schematic. I'll attempt to review the spec sheet you referenced, but my experience has been I quickly get lost with them. I just don't know enough of the terminology, etc to keep up. I realize this makes no sense to those of you with an understanding of electronics. But think of it as me asking why you don't understand advanced medical journals. Frankly my bigger concern is in actually making the item even if I determined the correct parts list. Again, like me wondering why you can't do a heart valve replacement...it's actually very easy to do, afterall sewing is simpler than soldering.

Hope this isn't taken as sarcasm, it isn't intended to be. It's just the best analogy I could come up with. But I do appreciate the input.

 

[dllubin]

Thanks. That was my understanding, however I have no idea how to determine the correct values to use for those resistors and capacitors, nor where each one would fit into the schematic. I'll attempt to review the spec sheet you referenced, but my experience has been I quickly get lost with them. I just don't know enough of the terminology, etc to keep up. I realize this makes no sense to those of you with an understanding of electronics. But think of it as me asking why you don't understand advanced medical journals. Frankly my bigger concern is in actually making the item even if I determined the correct parts list. Again, like me wondering why you can't do a heart valve replacement...it's actually very easy to do, afterall sewing is simpler than soldering.

Hope this isn't taken as sarcasm, it isn't intended to be. It's just the best analogy I could come up with. But I do appreciate the input.

Figure 13 and 16 in section 7 will show you what values of resistance and capacitance are required for a specific time delay or free running frequency so really not much in the way of any calculations required.

I actually like your analogy. Reminds me when I was a kid and decided to remove a wart on my finger. Taking the electrical engineering approach, I removed it with a diagonal cutter and cauterized it with a soldering iron. If I can do that, I'm sure you can sew the correct Rs and Cs on to the 555.

 

[Dr.Jeff]

Figure 13 and 16 in section 7 will show you what values of resistance and capacitance

I saw that when I reviewed the document. If I wanted to set two different times, one for how long it is open and another for how long it is closed, could I use two different resistor values for Ra and Rb in the schematic below? But which position is open and which is closed (R1 vs R2)? And how about the capacitor value (C), would it be the average between the two speeds, or ???

This schematic is the generic one illustrated in that document:

 

[Simon Oaten]

http://injectordynamics.com/articles/fuel-pressure-explained/

http://injectordynamics.com/articles/low-pulse-tech/

http://injectordynamics.com/articles/are-all-fuel-injectors-created-equal/

http://injectordynamics.com/the-library/


"measuring" a flow ..............IS NOT STRAIGHTFORWARD ........

differential pressure .......pump flow (with voltage), and injector open (with voltage) plus the "dead time" (with voltage).......its a 4-d table

 

[rachaeljf]

Jeff, the circuit from that video is pretty simple to make up and the components are cheap. I am entirely amateur, but I have made up some custom circuits based on Bowling & Grippo's MegaSquirt schematics using Veroboard and some of them actually work! Attached is a pdf of a Word document I used for making up circuits. The components are approximately to scale so that they can be laid out and moved around as required to fit on the board. This board is for two ignition drivers (IGBTs) and two injector drivers (FETS) for MS-ing a Punto GT engine. The lower set of components on the board are the original style MS VR conditioner, there are better circuits available these days.

 

[dllubin]

I saw that when I reviewed the document. If I wanted to set two different times, one for how long it is open and another for how long it is closed, could I use two different resistor values for Ra and Rb in the schematic below? But which position is open and which is closed (R1 vs R2)? And how about the capacitor value (C), would it be the average between the two speeds, or ???

This schematic is the generic one illustrated in that document:
View attachment 27651

See section 7.4.2 on the data sheet. The operating frequency is a function of the time constant C*(Ra+Rb). The duty cycle is a function of the ratio of Ra and Rb. They show an example that includes the math.

 

[Coupefan]

My tester is a slightly modified version of that Dino Segovis design. It works well. If you're adverse to soldering, build it on a proto board. I did it out of laziness. It still works the same. Pardon the dust, I haven't used it in years.

 

[Dr.Jeff]

a slightly modified version of that Dino Segovis design

Thanks for sharing the pics. My rig is a bit different because it is used with various types/quantity of injectors and for more than testing, so I had to make it flexible and configurable.

For my purposes the front half of the Segovis design (with the timer that controls the duration of the process, 1sec/5sec) would not be needed, I want to run them continuously. I realize his design can do that (override switch), but if that's the only way it will be used then there is no need for the timed function. So I was hoping it could be modified accordingly (more on that later). But I also like the potentiometers on the ADT schematic to allow variable adjustment of the frequency and duty cycle.

Great timing of your post as well; after Rachael's comment about using "Veroboard" I looked it up to find out what it is. Researching that lead to seeing the non-solder breadboard stuff you used. Frankly my solder skills really suck so this would be a big help.

In your last picture - are those MOSFETs, that act as relays? And you have one for each injector?
That Segovis guy has a note on his site about adapting the design to use with diesel injectors. They have a much higher amperage so the MOSFET on his schematic is replaced by another one that is rated at 75 amps:
https://www.allelectronics.com/item/mtp75n03hdl/power-mosfet-mtp75n03hdl/1.html
Even though I don't work with diesel injectors, I would like to be able to connect 8 of the low impedance injectors at the same time (about 50 amps). So that upgraded MOSFET might do it.

How did you modify his schematic?
Here is what I was thinking to eliminate the timer (but don't know if it is valid):

Basically cut off the half to the left of the heavy red line. But not sure if the capacitor C1 (blue circle) and/or resistor R2 (green circle) should be retained.

 

[Dr.Jeff]

I have made up some custom circuits based on Bowling & Grippo's MegaSquirt schematics using Veroboard

Thanks Rachael. I had to look up "Veroboard", that's how little I know about this stuff.

But that allowed me to discover other types of bread boards and aids to help assemble components. At this point I'm not sure if I want to just get one of the inexpensive little PWM devices online and add a solid state relay, or attempt to build something from one of those schematics. One problem is deciding which schematic to follow; all of them are similar and use similar components, yet they are all different enough to be confusing (to me anyway).

 

[Dr.Jeff]

See section 7.4.2 on the data sheet.

Thanks Don. The first time I read that I did not follow everything and misunderstood it. But from what you've said and looking again it is a bit clearer.

 

[Coupefan]

Jeff,

Yep, MOSFETs. I don't remember the part number, I already had them in stock in my garage. I used to do a lot of custom building in the early 90s, mostly laser entertainment projectors and whatever special effects device I needed, so I sitting on tons of crap..I could run a small Digikey outlet out of my garage. Whatever part I chose to use, they haven't been a problem. The average and peak current specs must be satisfied.

 

[Dr.Jeff]

early 90s, laser entertainment projectors

That brings back memories.

Thanks for the feedback. In my case the peak current is about 6 amps per injector (for the highest ones I deal with). And as mentioned I can run up to 8 of them at once. So it would be good for me to go with the larger capacity MOSFET.

 

[Dr.Jeff]

The operating frequency is a function of the time constant C*(Ra+Rb). The duty cycle is a function of the ratio of Ra and Rb.

By the way, once I understood this I think I realized why using a ready made PWM board may not be ideal. While the duty cycle could be adjusted with the potentiometer, the frequency will not change. Is that correct?

 

[dllubin]

By the way, once I understood this I think I realized why using a ready made PWM board may not be ideal. While the duty cycle could be adjusted with the potentiometer, the frequency will not change. Is that correct?

The frequency is a function of C*(Ra+Rb) so it would change. That may be why some designs use a separate 555 to set the frequency.