How to stop a hall throttle at rest putting out 0.8v?

[AZguy]

This is the basic outline - best to put a small (e.g. 0.1µF) ceramic capacitor from gnd to +5V close to the op-amp

[AZguy]

AZguy how are you? I’m just trying understand how to design out a problem I have. If I have 5v output I need to change it to 0v and if I have 0v I need it to be 5v. Basically I have a pressure sensor transducer that outputs roughly 0v (no pressure) to 5v (max pressure) but my controller needs to see the voltage in opposite, bare in mind all the variable voltages inbetween. I’m not sure a op amp could do this, but anything else I could use? A little lost and need some direction. Thanks in advance

This would do the trick:

[savroo]

AZguy how are you? I’m just trying understand how to design out a problem I have. If I have 5v output I need to change it to 0v and if I have 0v I need it to be 5v. Basically I have a pressure sensor transducer that outputs roughly 0v (no pressure) to 5v (max pressure) but my controller needs to see the voltage in opposite, bare in mind all the variable voltages inbetween. I’m not sure a op amp could do this, but anything else I could use? A little lost and need some direction. Thanks in advance

[pismocycler]

AZ
Not too nit too much. The diode is forward biased by the current flowing in the feedback resistors, so low current draw. I imagine the offset compensation resistor divider needs about 10X more current to avoid impacting the gain. In the diode circuit offset voltage compensation is coarse at best, I just want it below 0.6 V to avoid the controller lockout. Neither of these issues are critical so to each his own.

[AZguy]

I would avoid using the diode and just adjust the resistors

The op-amp has far more precision than the diode and especially over temperature where the diode will drift - not that it really matters since we're talking 100mV kind of range - mostly just that it's unnecessary since you can get there just adjusting resistors...

The OP's requirement was fulfilled by a simple two values of two resistors which is just sort of elegant more than anything else but fiddling values will get you there, just maybe not with that elegance...

[pismocycler]

Thanks AZ. I think I will change the topography and insert a silicon diode to produce an offset voltage to the op amp of about 0.6-0.7V (between a feedback resistor and ground). The diode will reduce the net offset to 0.18 - 0.28 V. Gain is not critical so about 1.1 is OK. I want to keep pots out of the circuit so I can surface mount the diode, resistors, and op amp. Then splice the board into the throttle wire harness. Might also consider a jumper to bypass the circuit back to stock if needed. But thansk for the idea in the first place. Simple and a lot cheaper than buying a BAC 4000/8000 just to tune the throttle.

[AZguy]

The topology should work but you'd need to change some of the resistor values and might benefit from inserting a potentiometer or two strategically in the circuit, or just have enough resistors on hand to fiddle with them

If you measure what you have and give an idea of where you feel like you need to end up I can churn numbers for you

[pismocycler]

I have a throttle problem where I think my zero offset voltage of 0.88V is too high for the Sur-ron controller. Your circuit looks like it might fix this by lowering the offset voltage (I think I need 0.7 to 0.75V). Do you think this will work? I think I can prototype a pc board and use surface mount op amps and resistors so it could be mounted on the bike in the harness

[AZguy]

Pots are fine although if I were going to utilize them I'd let my OCD put in two - (a gain and offset, I think you only have offset) so you can adjust both the top and bottom limits

[savroo]

AZguy thank you so much for your support, nice to know I can just use 1 op amp (2 op amps in one chip) I am still using 2 separate ones for now as I never knew anything better.

Regarding the pot or resistors I still prefer using the pot as it gives me some fine tuning. I’m also using an additional pot and is on the dashboard to limit max power to the motors which is wired in as follows and link for further info. It works really well.

https://electricbike.com/forum/forum...d-modification

[jlh]

I love it! K.I.S.S. has always appealed to my way of thinking. Thank you for the explanation and lesson. MCP6041 here I come!

[AZguy]

That LT part is overkill for sure (very expensive!), but doesn't really matter

The three are just all connected with outputs more or less in parallel to the "master" which would ease how much current each one delivers but the 200Ω resistors on the outputs will limit that current anyway and keeps the amps from "fighting" with each other and if they're there might as well use them I suppose - definitely don't want to leave their inputs unconnected regardless. It might make sense if they were expecting driving a lot of capacitance but I wouldn't expect that...


I guess I lean to the single op-amp solution I put forward based on the cheapie MCP6041, but then again it's mine so I'm not unbiased LOL. It does lack the adjustments although they'd be easy enough to include, they just don't seem necessary with a decent opamp... Two (or more) op-amps don't help anything here, just a different approach.

It's a lot cheaper - the MCP6041 is less than $1 and the LT633 is >$14(wow!) and even the TLC2272 is >$2.50... it's very available too (in DIP - much easier to solder too), not so much the LT

Plus, a fellow built it and tried it so it's a know good, at least in his application. I wouldn't bother with trimpots but then again I've got a decent selection of resistors and could fine tune them if need be but my dim recollection is I designed it taking into account tolerances, etc. to ensure it would goo all the way to 0V and 5V without any significant dead play.

And not that it makes much difference, but I gravitate towards "elegance" and simplicity and there's something appealing to the eye about jut one amp, and only four resistors and only two values... but that's just "pretty" and doesn't have anything to do with functionality...

[jlh]

Reaching out to AZGUY.
I am tuning my grandson's electric Gator and was looking for a way to substitute the pot for throttle/speed control with a hall effect throttle. I'm using a very basic PWM controller with no soft start or ramp up time. First I found the quad op amp design that I presented here then Savroo's dual design and then your design.
I don't grasp the quad design as to why the additional 2 op amps.
If you could expand on the why and pro's / con's of the 3 versions I would enjoy the education.
I enjoy browsing the posts and enjoy seeing all the talent that is gathered.
Regards

[AZguy]

The TLC2272 is a dual op-amp (i.e. there are two devices in one package) so only one set of power pins for two devices that are in one package

[savroo]

For everyone that has come to this webpage, you can see above op amps used to convert a Hall effect to give 0 to 5v reading instead of 0.8 to 4.2v approx. I’ve been using the above diagram but my son’s car is ready for more battery voltage. I revisited the op amps it was always difficult to calibrate with the pot and was abit sluggish to get to exactly 0v when you let go of the throttle. This is me being thick but the first op amp in the wiring diagram does not show the powered wires to power one of the op amps pins 4 and 8. I think I built at least 3 circuits with new op amps this week as just couldn’t get them to work perfectly I’m thinking I have blown the op amps. Anyway I just gave it a go and wired the op amp in the diagram with power pins 4 and 8. It now works perfectly, is not sluggish and easy to calibrate. I’ve added the wiring diagram to exactly show how to wire up.

This is someone who can solder but has got minimum experience of electrical engineering, so was just following the wiring diagram. See diagram and when I need to build another one will come back to this page :-)