Alternative controller

[bertiedog]

Codar did not do it in a really sophisticated way, they simply used a log law potentiometer instead of a linear pot, but it gave slightly better low speed control, to which was added pulses etc.

Stephen.

[bertiedog]

i remember discussing this with a supplier, it may have been Codar, who said non linear scales on the panel put people off, they expect the markings to be like a clock, regular segments, and when a scaler is used the scale is cramped at the the top end, with big segments from 0 upwards, making it look funny!

 

I think know some top end British Hi-Fi makers in the 1970's had non linear volume controls, but marked the front plate with linear segments, just to make it look right.to the owner!!

 

The top American maker Marantz put no markings on the volume control at all because of this, as all the other controls have linear segments, and it would look odd.

 

Stephen.

[relaxinghobby]

I going ahead and using the Maplin motor speed controller, I'm preparing it's case.

 

The 1/8 th inch balsa sides to my home made box seem a bit flimsy so I've stuck another layer inside to stiffen them up.

 

 

The picture shows the circuit board fitted into the box, along with a Double Pole Double Throw switch for reversing the current to the track and

a push button for a voltage boost feature I intend to add.

 

You can also see the cheapo spring clips from Tesco which have turned out to be very useful and versatile.

[Belsay Lad]

Regarding Codar Controllers:- I still have two original 'Tec-Mod' controllers purchased in the late 1970's still giving sterling service on my N Gauge layout. Many years later after Codar ceased trading I needed another controller and bought an ECM 'Compspeed' Simulator with very similar controls to the Codars but with the addition of an 'Accelaration Rate' preset.

However, they are two totally different beasts - Codar=pure DC, quiet motors and cool running. ECM=PMW with feedback, much better slow running\speed control but at the expense of motor noise and quite significant motor heating at slow speed. And this is with 'traditional' motors.

 

However, another plus with the ECM is that they incorporated short circuit protection.

 

Probably should be a new thread but I'll chance it anyway- is there a current circuit diagram available anywhere for a 'Codar Tech-Mod' type controller (preferably with short circuit protection) as Codar seemed to have disguised certain key components of their design, obviously to protect their product.

[bertiedog]

I have one of the original Codar circuits stored away, I will try to find it. They did fiddle a lot with the designs, as newer components became available they were incorporated with model number changes.

 

Stephen.

[bertiedog]

I believe this is the original circuit for Codar, no evidence it's original or accurate, I have not checked it through or built this version exactly, but a quite look seems to show it is a working circuit.

[Belsay Lad]

Hi Stephen

 

Many thanks for your answer, most helpful. I'll give the circuit a go as soon as I have a chance and let you know how I get on.

 

regards

Eddie

[bertiedog]

I have another copy with proposed changes, no meter, components marked,and a LM317 regulator to provide more protection, but I do not remember testing it out, so no G/tee as to the mods working, but it should

[Gordon H]

I have another copy with proposed changes, no meter, components marked,and a LM317 regulator to provide more protection, but I do not remember testing it out, so no G/tee as to the mods working, but it should

The electrolytic capacitor symbols are drawn the wrong way round, though the '+' signs are shown in the right place. The 'empty box' half of this symbol variant should be the positive, which is intended to obviate the need for a '+' sign at all. Sorry to be pedantic about it, but a similar situation arose in a recent Railway Modeller article diagram, and this month's edition carries a correction for it.

[Belsay Lad]

Hi Stephen/Gordon

 

Thanks again to both of you for your replies. The second circuit looks like what I would go for, having taken Stephen's comment about it not being tested, but I am happy to give it a try. I have just checked out Squires Electronic Compoments Catalogue and confirmed that all the components etc are still available so I'll pop in order an over the next week. I did have a circuit diagram for a quite sophisticated controller dating from (I think) the early 1970's but some of the semiconductors are now apparently defunct!

 

Eddie

[bertiedog]

Try Ebay for the components, and never worry about types no longer made, generic types exist for almost all transistors. The 2N3055 is available for 50 pence up in the plastic pack form, TIP3055, make sure they are on large heatsinks though. Almost any equivalent transistor can replace the ZTX 450, which is available anyway.( I can't see why another 2n3055/TIP3055 would not work....?)

 

The first circuit has no regulator, but again the low cost of adding it seems worthwhile. The LEDs are more for show than anything, I do not remember them on a Codar I had, but I am assured this id the circuit they used,

 

Stephen

[bertiedog]

Tidied up version if anybody tries it, the caps are shown correctly. The LEDs from left show basic,power on, then power on, or LED off, with short, and the final one shows power circuit to loco. Very cheap to build, try Veroboard or the patch boards with wire links. Should suit any decent loco that needs DC , without pulses, which can over heat small motors or coreless types, which should be safe on this controller.

 

An older controller could supply the 16 VAC to the rest of the circuit, and the regulator can be dropped out completely.to save cost.

I doubt if the circuit is copyright to Codar, but if so is provided for service and research purposes only.

Hope this did not highjack the Maplins content...

Stephen.

[Gordon H]

Tidied up version if anybody tries it, the caps are shown correctly.

Ah! Much better...

 

Does make me wonder though, whether it would be equally effective to use the LM317T itself (or possibly a second one) as the output stage. After all, the rest of the components are only there vary the voltage at the base of the ZTX450 to set the overall output level. A similar effect could be created by using the LM317 ADJ pin. You would get the additional benefits of the LM317's own internal protection capabilities too.

Another more readily 'do-able' alternative would be to replace the ZTX450/2N3055 combination with a single TO-220 packaged Power Darlington transistor such as the BDW93C. Much more convenient to mount than a TO-3 package.

Just a thought...

[spamcan61]

Ah! Much better...

 

Does make me wonder though, whether it would be equally effective to use the LM317T itself (or possibly a second one) as the output stage. After all, the rest of the components are only there vary the voltage at the base of the ZTX450 to set the overall output level. A similar effect could be created by using the LM317 ADJ pin. You would get the additional benefits of the LM317's own internal protection capabilities too.

 

 

These LM317T regulators only go down to about a volt minimum on the output side though IIRC, so you can't directly do 0-12VDC, not sure what proportion on locos actually still move at around a volt mind you.

[bertiedog]

Beat me to commenting about the min regulator issue with the LM317T, a lot of modern motors will move on the minimum especially coreless types. You can just add resistance, but if high currents are drawn it gets a bit hot.

Are there regulators (not expensive types) that do go from true Zero?

By the way I did not add the regulator myself it was proposed on a forum listing discussing the Codar controllers, there are other circuits around as well, including PWM types from them.

The basic circuit without the regulator is simple and has the acceleration control, and is very un-fussy, and easy to build. (and cheap, under a fiver's worth really).

Stephen.

[bertiedog]

The bottom voltage is actually 1.25 volts, (by spec.), and medium Mashima's move on it, (no load though), just tried it on Lab supply. Under a light load it does start with a bit of a rush as it goes up.

If your more serious about slow speed then PWM is better, but may induce a bit of motor noise.

Stephen.

[Gordon H]

These LM317T regulators only go down to about a volt minimum on the output side though IIRC, so you can't directly do 0-12VDC, not sure what proportion on locos actually still move at around a volt mind you.

The usual trick to overcome this is to add a couple of forward biased rectifier diodes to the output to drop the minimum back to zero.

[bertiedog]

I had wondered about the use of series diodes, should work fine , there is nothing in the spec sheets against it, the only restriction generally overlooked is there must be a 5ma current flowing, fully met here.

A simple controller with the LM317 seems to be as good as the Maplin,and as long as there is no requirement for the acceleration control, then the entire Codar circuit can be dropped , and a variable resistance used to control the voltage as per spec sheets circuit suggestions. Many sites have small variants on the circuit needed.

The LM317T plastic pack,with heat sink tab, is available on ebay from about 40 pence inc., postage, .......I just ordered some.(5 at 99p). myself.

Stephen.

[bertiedog]

This is about the minimum with a LM317T, the diode is protection, the 0.1uf marked should be close to the chip. the other capacitors could be almost any value in excess and work, the input capacitor could be 10,000uf or more. Input voltage 16 VDC min, (do not feed 16VAC input!!), up to about 20VDC It requires no further protection the chip will shut down on overloads. Use a good sized heat-sink.(plain aluminium plate)

 

Add diodes to output if the non zero voltage causes any bother, and add a suitable centre off reversing switch. The circuit is so simple it barely needs a board, use an electrical screw strip (mains type) to support the components..

[JohnnyDMonic]

Hi there,

 

I am the person who drew that Codar schematic. It comes from a different forum here:

 

https://forum.allaboutcircuits.com/threads/model-railway-controller.3185/

 

It was reverse-engineered from a Codar TEC-88 which my dad had since new (see image attachment). It is pretty simple, R2 is the main speed control, R7 is the "simulator" control (basically adjusts the rate of discharge of C1. Switch S1 turns the simulator on/off.

 

I have a feeling I added R3 because I made a copy of this controller for my Dad which had a walkaround remote control. The addition of R3 makes the loco stop if the remote control is unplugged. Either that, or I was adjusting the linearity of the speed pot to make it have more resolution down low. Don't take my word for this, it is just a distant memory from 13 years ago.

 

The copy I made also had a switch to change from un-smoothed DC (how it was on the original) to completely smoothed DC using large filter capacitors (at my Dad's request, for coreless motors). The reversing switch was swapped for a relay with appropriate control circuitry, all to enable it to work from a remote control. I believe I still have the schematic somewhere. If I can dig it out I'll post it up here.

 

For people asking about short-circuit protection, that's what F1 does. It is a poly-fuse (resettable fuse). I believe on my copy there is also a glass fuse on the primary side of the transformer as well.

 

 

[sharris]

On 11/07/2011 at 21:08, bertiedog said:

Tidied up version if anybody tries it, the caps are shown correctly.... 

 

 

I know it's rather late in the day (8 years late!) but since JohnnyDMonic just re-opened it, it's the first I've seen. I'm surprised by the small value of the capacitor to the left of the LM317 - I would expect something  much larger, more like 1000uF, to smooth the output of the bridge rectifier to DC before applying it to the regulator, in-fact, as you have with the second (13 July) minimal LM317 design you showed.  

 

If I couldn't find a ZTX450, the 2N3055 would not be a suitable substitute. The darlington emitter follower, which the two transistors create in this circuit have a current gain which is the combined gain of the two transistors. 2N3055s have a very low current gain (typically specified as 20-70) while the ZTX450 has a higher gain (typically 100-300) - worst case a darlington made from a pair of 2N3055s would only have a gain of 400, while a ZTX450/2N3055 would be 2000. The ZTX450/2N3055 combination has a higher input impedance which better suits the component values for the speed and inertia control pots, and surrounding resistors and capacitors. Replace it with a 2N3055/2N3055 pair and you'd have to reduce the values of the resistors considerably and increase the capacitor values - and you'd need a bigger box! 

 

Incidently, Wikipedia tells me that 2N3055s are widely counterfeited with underpowered dies inside the packages, so you might want to buy from a reputable supplier rather than a random Ebay seller. 

[JohnnyDMonic]

If I were to make another one, I'd be tempted to try a single TIP120 instead of the ZTX450/2N3055 pair. They can be had for a little over 50p.

[sharris]

1 hour ago, JohnnyDMonic said:

If I were to make another one, I'd be tempted to try a single TIP120 instead of the ZTX450/2N3055 pair. They can be had for a little over 50p.

 

Might work as-is, and as you say, it's a cheap solution, but with a minimum Hfe of 1000 vs the combined original of 2000, you *might* not get the same maximum current capability with the components as specified and you may want to reduce the speed control pot and resistor values by about half. I say *might* because these are minimum specified values and if you get a good one the gain might be somewhat higher and it could work to the full power of the original anyway.