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  #1  
Old 10-21-2004, 08:29 PM
slotfarm
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Default schematics and instructions for electronic controller

I have talked a little about an electronic controller both here and in the 1/43 forum. Some have asked me to post schematics so they can try it out. I am posting it here. Please feel free to use these to make your own but I would ask you not to sell them. I have put a lot of time in in the last year to design this and some follow ons and plan to produce them. With that prenote now the fun stuff.

I started thinking about this after I got into the hobby about two years ago and started with 1/43 cars, then added HO Tjets and magnet cars. I then got an Artin 1/32 set. I enjoy racing all the cars. My personal favorites are the 1/32 and the Tjets. I really liked the 1/43 size but controllability wasn’t as good. Another problem was that I wanted to replace the stock controllers. I did get five Parma controllers 45-60 Ohm. This worked ok but for the Tjets a 125 Ohm controller works much better and the 1/43 Artins need a 7-15 ohm resistor. This meant to race all my cars and tracks I needed many controllers with different resistors. I thought of going with a diode controller but you still want to modify them depending whether it is an 18 volt HO setup or a six volt Artin setup. I also happen to be an Electrical Engineer with some experience in analog design so I started thinking of how to do a version with more control.

What I have come up with is a circuit that you hook up to any resistor controller (from 10-200 ohms) and can run any car (well the high powered ones need a really good heat sink) but at least any RTR car and a lot of others. It can be modified even for wing cars. The adjustability is outstanding. You can adjust the top speed and the starting speed. The schematics I’m posting today have these two adjustments. It feels a lot like a diode controller as it controls the voltage to the track.

I have working at home but not yet ready to post one with brakes. You get brakes even with a non-brake controller. With brakes there are two adjustments one for sensitivity and the other for active braking. Active braking means that the car is actively decelerated when you slow the car down on the controller. Some people like it, some don’t. I have a PWM version that is much cooler especially for the high powered cars but it is still in development. The last thing to add is the response curve. I would like to be able to make it linear or exponential (like an audio taper pot). The exponential gives more control at low speed for road courses. I then have a digital version in the early design stage that lets you save the settings for different cars and controllers.

For those who don’t like to build from scratch I will have a circuit board in a couple of months followed by a kit and then the assembled version.

So back to this design. Here is the schematic. The URL is to a larger schematic that is easier to read but bigger to download.



http://spotten.org/slotcar/basicctl.JPG

To make this controller just hook up the componenets on a breadboard or proto board. The pots can be mounted in a project box to give a finished look. I don’t have a very finished look yet so I don’t have any photos.

The basic controller uses three op-amps of a quad op-amp IC LM324 available at Radio Shack. It also needs a PMOS FET. This can be ordered from Mouser or DigiKey or JameCo. The 324 op amp is also a lot cheaper from the above sources than from Radio Shack. Get a good heat sink as well.

The first two op amps feed a current through the controller resistor and measure and amplify the voltage. The two potentiometers control the top speed of the car and the starting speed, or speed you get on the first band of the controller.

The third op-amp and the PFET make up a unity voltage gain buffer that provides lots of current to the car. That’s the simple description.

Here’s a little more in depth. The first op amp creates an appx 4 Volt reference using a regular diode (any will do). The 4 volts is applied across a voltage divider circuit consisting of the controller resistor and the 1K resistor. This creates a voltage that is at 4 Volts when the controller is pressed all the ways and is zero when released. The potentiometer adjusts the gain and adjusts for different controller resistances and also adjusts the starting speed. This voltage is then sent through the second pot to provide top speed adjust. The output feeds into the amplifier/driver section.

The 39K, 10K resistor and 10 uF cap on the output divide the output voltage and filter it so it is in the same range as the input. The third op amp compares the voltage from the input section (the desired voltage) and compares it with the output voltage. If they are not the same it adjusts the drive to the PFET to turn it on or off more. It is a nice simple circuit but the results will surprise you.

One not about the feedback. I use a diode based reference at the first rather than just a voltage divider because this makes the control voltage (the reference) mostly independent of the supply voltage. This means if the power supply voltage droops as an unregulated supply voltage will, the output you get to the car does not change. It also helps in sizing the resistor that is in series with the controller resistor. 4 volts allows us to use a standard ¼ W resistor instead of a bigger one. To match the output voltage we divide it by four. This circuit will work with 20 volt Ho supplies and six volt Artin 1/43 supplies. It also means that you can have one supply for a track that runs 1/43 and 1/32 and the max speed plays a double role as an adjustable voltage. You can set the max at the main supply and everybody can adjust their own.

Please feel free to e-mail me questions as slotfarm_at_spotten.org (replace _at_ with @) or post questions here.

Warning. This is a fun controller and you will be hooked and want to make them for all your cars. In about a month I will post the schematics for using a second quad 324 and an NMOS FET to add brakes.

You should make sure you put a fuse in-line because the PFET can conduct much more than 2A.
Hope you enjoy and tell me how it works. I’m going to work on refining it now.

Slotfarm (Reed)

Slot because we love slots and farm because we live on a one-acre mini-farm.
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  #2  
Old 10-21-2004, 10:00 PM
idontbelieveitsbutter
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Wow

Nice work...I'll be giving that a go...
Any chance of a parts list

cheers
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  #3  
Old 10-22-2004, 05:46 AM
MaxConfusion
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Nice work Reed!

Thank you for sharing the schematic :-) I'll give it a try too.

The only part that I am not sure of is the PFET type... which one did you use?

Gale
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  #4  
Old 10-22-2004, 06:41 AM
slotfarm
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I have used several. Go to Mouser or DigiKey and look for PMOSFET in T0-220 package with on resistance of less than 0.5 ohms. Some I have will go down to under 0.1 ohms.

I have an order here from MOUSER with two part numbers. One for PFET and one for an NFET. You can type the part number in to find which one is which.

Fairchild NDP6020P
Fairchild NDP6030BL

Type the NDP into the MOUSER part number at www.mouser.com and it will have a description. Mouser is also great because they don't have a minimum order and shipping is usually $3-6 on small orders if you choose priority mail.

SlotFarm (Reed)
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  #5  
Old 10-22-2004, 07:35 AM
MaxConfusion
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Thank you Reed, that's what I needed :-) I'll let you know how the building goes.

Gale
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  #6  
Old 10-22-2004, 03:40 PM
slotfarm
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Default Re: a modification and how to adjust

Hello,

Initial adjustment

Two things. One is how to adjust the controller. Since there is such a wide range of controllers and cars and voltages, the following simple process helps get you at a starting point. I'm looking at the circuit to see if I can make it simpler.

1. With the resistor controller at full power on, put a car on the track with the drive wheels in the air and adjust the top speed so that turning it more doesn't get anymore speed out of the car. Then back it to where it slows just the tiniest bit. This is a good starting point for max speed.

SlotFarm

Slot because we love slot cars.
Farm because we have a one-acre mini-farm
2. Now put the resistor controller at the first power band (slowest car can go) and adjust the sensitivity till you get the starting speed you want.

You will notice that changing the top speed a little will not noticeably change the starting speed but changing the top speed a lot usually requires a little change in the min speed setting.

Modification

I will post an updated schematic in a few days with some improvements but here is one you can do now. It gets rid of an AC oscillation that is not fatal but you will hear your car singing.

On the current schematics, there is a wire from pin 1 on u1a to the gate of the PFET. Replace the wire with a 10K resistor. Then put a 1-5 uF capacitor from the gate of the PFET to ground. This forms an RC filter to get rid of some oscillations that can happen. The problem is the the gain of U1a and the PFET is very high and you can get AC oscillations.

Future Mods and updated schematic

With the current schematics there is a little bit of power always delivered to the car. This is due to two things. One is the diode connected between the track red wire and the ground of the circuit. This is there to protect the analog circuit from reverse connecting the wires to the track. I didn't put it in the output so that full power can be delivered to the car. A side effect is that there is always 2-3 volts at the car. I have a mod that I will verify and publish soon. The second thing that causes the power is that the op-amps don't pull all the way to zero because they are not CMOS outputs internally. So the output of U1b only goes to around 0.7 V. I have a mod I also want to verify for this and then I will post updated schematics.
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  #7  
Old 10-22-2004, 09:17 PM
idontbelieveitsbutter
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Default Re: a modification and how to adjust

Hey...I have it figured out..exceopt were does the 2nd pot go?
I might wait till you post the mods till I build it...I dont want to keep going to the shop...lol
and are they rheostats at r6 and inbetween cltwhite and cltblack?

cheers
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  #8  
Old 10-23-2004, 04:08 AM
slotfarm
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Default Re: a modification and how to adjust

There is a 50K pot attached to pin 7 of IC1 to adjust top speed, and another one attached to pin 7 as a rheostat (adjustable resistor) to adjust the minimum speed. The rheostat shown between ctrl white and ctrl block is just there to indicate that that is where the resistor of the controller is hooked up. As a normal hookup black to black and white to white.

As far as the other mods go, they should just be a couple of days. You might try breadboarding this as then changes are easier. The circuit works fine as it is but some power is always applied to the motor. The other mods fix that.

Reed
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  #9  
Old 10-30-2004, 09:11 PM
slotfarm
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Default updated schematics and parts list

well here is the updated schematics as promised and a parts list. Not that much has changed just an RC filter between the last opamp and the PFET to reduce oscillations and NPN transistors added to the outputs of the other op-amps to provide increased drive current or provide output to 0V. The 324 op-amp will only drive down to about 0.7 V.

I have a version with brakes designed and built and tested on my testbed (with a 10 ohm resistor as a load to represent the car). I will be testing it out live for the next few weeks and then will post the schematics. If you build the version here, then all that is needed to upgrade is to add some more circuitry. Two more opamps and an NFET to do the breaking. So if you leave room on your board for another op-amp and NFET then you can build this now, enjoy it and then upgrade when the braking version is completely tested.

Pointer to schematic
www.spotten.org/slotcar/u...roller.JPG

Parts list

Parts List for no break electronic slot controller.
Note: there are gaps in the component numbers but this is so it matches with the brake version.

Resistors are all 1/4 W resistors of the size listed on the schematics
Potentiometers are better if audio taper but linear will work.
C1, C4, and C7 are electrolytic caps of the indicated size and 35 V rating
C2 is tantalum (circuit will work without but helps with oscillations)
C5 is a ceramic disc capacitor.
D7 is a 1/4 watt rectifier diode. Most will work.
D4 and D1 are 1/4 watt zener diodes of the indicated voltage.
Transistors Q1 and Q2. most NPN's will work.
&nbsp &nbsp &nbsp &nbsp The one I have used is 2N3904. The only requirement is delivering ~10-20 ma of current
Transistor Q5 is an PMOSFET. Two part numbers that will work with the corresponding suppliers:
&nbsp &nbsp &nbsp &nbsp DigiKey IRF9520-ND (manufacturer is international rectifier)
&nbsp &nbsp &nbsp &nbsp Mouser NDP6020P (manufacturer is Fairchild)


Good Luck and Enjoy and let me know how it works.

SlotFarm (Reed)
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  #10  
Old 10-30-2004, 09:22 PM
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Default Re: updated schematics and parts list

I can't wait for the final version, I have several Artin and SCX controllers that I can convert.
Thanks for the great work!!!!:hat
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  #11  
Old 10-31-2004, 09:25 AM
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Default Re: updated schematics and parts list

Can you give us a little more info on the "quad op-amp IC LM324" maybe a digikey part number, thx.
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  #12  
Old 10-31-2004, 10:48 AM
pmarchand
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Default Re: updated schematics and parts list

Hi Brent;

Thsi should be it: www.onsemi.com/pub/Collat...M324-D.PDF

Part number will vary depending on the package you take (these come in 3 different packages).

Here is the page at Newark

www.newark.com/NewarkWebC...n&x=27&y=6

-P
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  #13  
Old 10-31-2004, 10:52 AM
slotfarm
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Default Re: updated schematics and parts list

You can buy it at Radio Schack for a 1.50

The cheapest version at Digi-Key is .45 for 1 and
has Digi-Key part Number;
296-1391-5-ND

Actually if you have any quad op-amp laying around it will probably work. The LM324 is one of the cheapest and I picked it for the low price and designed with it.

Let me know of any more questions or any success anybody has with the design.

SlotFarm (Reed)
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  #14  
Old 11-01-2004, 05:53 AM
slotfarm
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Default useability mods

Hello,

After more testing with 12 V Artin 1/32 on a Oval track I have a few more mods. They are simply removing or changing a component value. I explain below what they will do. There shouldn't be many more mods but part of the reason I got it out their is so it can have more compatibility testing with different systems. If you have any problems or questions let me know. If you have the luxury this can easily be wired up and run on a PROTO-Board or similar jumperless breadboard. That is how I am prototyping it till I get a board layed out. Don't want to do that till I get the brakes fleshed out.

I have basic functionality with the adjustable brakes working. However there is quite a bit of tweaking to do. Don't expect schematics of that for a month. I would like to have them in time for Thanksgiving but with other things (work, family) may not make it. Once again let me know of successes and problems.

Useability mods.

1. Make C4 into a 0.1 uf ceramic disk capacitor. (otherwise there is a delay from when you release the trigger to when the car slows down) Might even try a 0.047 but watch out for oscillations. Depends on board design.

2. Remove capacitor C7. Was a carryover from a PWM version and is not needed and in some cases can start oscillations. If it's not causing problems you can leave it. If the car makes noises when it's not running try this one.

3. remove R4 and make R3 into a 19K or 22K ohm resistor. As currently implemented most of the useful adjustment is in a very small range of the potentiometer. This spreads the adjustment out over more of the pot making it easier. Also removing R4 allows a higher min-speed (up to the max speed). This is useful on an oval where you set the min-speed to be the speed the car will hang to the turn and then use the rest in the staights.


SlotFarm (Reed)
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  #15  
Old 11-14-2004, 10:59 AM
idontbelieveitsbutter
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hi...hows the update for the brakes going

cheers
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