In need of a DC amplifier...input 0 to 7 volts, output needs to be 0 to 16 volts...

Allow me to explain..

I have on going project, that does not involve a Propeller or Stamp, so I did not what to put this thread on those forums. So...., I have built a few stand on golf carts, to carry me and clubs around the golf course. I use 24 volt power chair motors from Ebay, design my on PWM and gate drivers, using 24 volts. Carts use front wheel steering, with handle bars, like a bicycle.

Now, I thought I would try a joystick application, to avoid the making from scratch, the front wheel steering (aka rack and pinnon jchain drive). Instead by using the drive motors to steer left, right and reverse. And using large type of casters for the front wheels. So, I went on line and found a joystick circuit that I built and designed
for a PCB . This circuit is called "Dual Channel Interface Board", from a company in England, called 4QD dated 14 April 2000, Issue 5. You can google that and see the circuit if you look around for it..and I have emailed with them, and there is no problem in me using that

As I said, the joystick circuit works very well, but...ya, here is the operates on 9.1 volts, so the output for speed on both outputs will only approach 7 volts, and I need an output from 0 volts, at standstill to 16 volts, full speed to gate drive my very high amp, MOSFETS. Right now, I am using a handlebar twist drive throttle (a variable hand gripe potentiometer..5K) to the threshold pin 5 of a 555 to develop the necessary PWM, which in turns drive a HCPL3120, one for each wheel.

If I try to run the 555 on the 7 volts I do not get full speed...and I have tried to increase the voltage running the Duel Channel circuit, but that causes the circuit to no longer give me any output in "reverse joystick". Some sort of imbalance in that Duel Channel circuit op amps, I believe.

With everyone's vast knowledge, would anyone know of a..lets call it a "variable DC to DC driver/amplifer circuit, that would take a variable DC voltage of 0 to 7 volts and give me a corresponding variable DC voltage of 0 to 16 volts out?

I could send you some photos of what I am working on and doing, if I knew where to send them. Please understand that this is just a hobby for me....sort of reinventing the wheel....but it is fun. Especially, on the golf course, others ask, where did you get that, that is cool, and I get to say, well I made it....!

BTW, the 555 runs on 16 volts, which does give me the necessary PWM at a set frequency of around 10Khz. The higher frequency to avoid motor scream noise due to the PWM. Anyways, the HCPL3120 is a 2.5 Amp Output Current IGBT Gate Drive Optocoupler. I am using it to drive two TrenchGate Power MOSFET IXFN360N10T, one for each motor/gearbox which will handle 360 amps, but my motors do not draw that much...up hill with me on, around 50 amps...each. I did design the snubber circuits, and the forward/reverse/electric park brake, when the cart stops moving to lock the wheel, until throttle is once again applied....

I do not have alot of savy with op amps. The circuit that I built for the joystick came from someone else, as I mentioned above. I would appreciate some accurate detail information or even a circuit that possible you/someone has designed and used.

I will keep looking around, and thanks for your time...Dennis


  • It should be easy enough to modify the 555 circuit to accept a lower signal. Please attach a schematic, as a pdf or png, of what you have at the moment.
  • Try using relays. Or, if they are too slow, a high-voltage transistor(can you get a 12v transistor?) that accepts 9v as a trigger.
  • Peter JakackiPeter Jakacki Posts: 8,854
    edited 2019-06-01 - 01:52:45
    I must admit Denno, I read this the other day but I couldn't get my head around it all. There are lots and lots of words, and absolutely no diagrams or photos.
    Not really sure what you want although scaling 0..7V to 0.16V is neither here nor there, it is dead simple. You just need an opamp in a non-inverting configuration, that is feed the 0..7V to the + input, and use 2 resistors to tset the gain with R1 from - input to output and R2 from - input to ground. The circuit needs a gain of 2.2857 which is set by the ratio of R1/R2 but the non-inverting configuration already has a gain of 1 so R1/R2 = 1.2857. Closest standard resistor values for R1/R2 would be 110K/86K. While that is an answer I still don't think your question is the right question, we really need more information in the form of diagrams.

    Here's the circuit. An LM358 is cheap and works up to 35V but will drop and 1.5V from the top rail so you will need at least 18V supply. If your supply is 16V then just use another rail-to-rail opamp. The dual opamp in 8-pin footprint is very common and so you can drop in one that is suitable.
    594 x 310 - 11K
  • Denno,

    You seem to have a fair handle on electronics, especially having built parts of this without releasing to much magic smoke for the power parts. OpAmps should not pose a problem with a bit of information. What you are looking for is a scaler to change from the current output range to one compatible with your drive electronics. There is an excellent work out there from TI called OpAmps for everyone. An older PDF version seems to be readily found as well as a later edition for about $70USD via amazon for example. The link to this is and there is much in there to help you with your design. Admittedly a bit of overkill but a good reference. Another source of information can be found by looking up the name "Bonnie Baker", an applications engineer for TI and some others along the way. She has books, white papers and lot of EDN/EETimes/etc articles, all regarding analog systems including ADCs/DACs, I/O conditioning etc. Remember, (I know, maybe not politically correct but...) Google is your friend.

    Of course, if you decided to drop a propeller into the mix, you could probably come up with lots of ideas to play with....

  • Thank you all for your help. Attached is two files (photos). The second one is of the 555 PWM which in turns drives the HCPL3120 opto gate driver. My poser mosfet do require a full 15 volts on the gates to pass full 24 volts to the motors. You can look up the specs from my previous post. So that PWM board runs on 16 volts Vcc. I use a 317 voltage regulator to drop the 24 volts down to 16 volts. The motors require 24 volts. Lowering the voltage from the twist grip throttle will lower the PWM output of the 555. I am referring to the duty cycle output, which in turns drives the opto in the HCPL3120.

    The first photo is of the joystick circuit. I have this built on a PCB and it works very well, but only at 9.1 volts, as it was designed by someone else. Increasing that voltage up to 16 volts, does work, but in that circuit, something goes "off balance" and I get no reverse from the joystick.

    Would like to hear what you think...I have also included a couple of photos of what I now use on the golf course, which uses handlebar steering...

    Peter Jakacki, I will breadboard the opamp...sometimes, I do not see "simple", right in front of me...thank you for that eye opening....LOL

  • kwinnkwinn Posts: 8,440
    edited 2019-06-02 - 02:04:30
    Redacted earlier post. You will need a higher control voltages to have the 555 cover the PWM range. I am wondering though if it would possible to replace most of the analog circuitry with one or two 555 timers. A microcontroller could certainly read two potentiometers and do the job easily. Forward, reverse, turn left, turn right, rotate CW, rotate CCW would be a breeze.
  • evanhevanh Posts: 8,620
    edited 2019-06-02 - 02:11:24
    I suspect you can get what you want just by moving the 470R resistor (on pin 7 of the 555) from the 16 volt supply to the 9 volt supply.

    PS: You could add a trim pot, say 0-100R, to that same resistor for centring too I think.
  • evanhevanh Posts: 8,620
    edited 2019-06-02 - 02:18:11
    Or, instead, stay with the 16 volt supply and increase the 470R. This might be better so to keep the toggling noise out of the joystick op-amp circuits.
  • evanh wrote: »
    I suspect you can get what you want just by moving the 470R resistor (on pin 7 of the 555) from the 16 volt supply to the 9 volt supply.

    PS: You could add a trim pot, say 0-100R, to that same resistor for centring too I think.

    I think you might be right. Worth a try
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