Massoth 8156501 decoder use with RC servo

granddad

granddad

Registered
Hi,
I have a spare subject decoder, and I have been 'playing' around with it ::)
The manual mentions use with RC servos, but there is no connection diagram.
Now, all of the RC servos I have ever used have three connections, +, -, signal but the decoder in question has only two.
Could someone enlighten me as to how I would use this decoder with an RC servo please, regarding connections and programming of CVs 121,122,123.
TIA
Martin
 
Sorry Martin, I have no idea regarding the connections. May I suggest you send an email to Massoth on hotline@masoth.de and ask them directly.

It would seem that the Servo operation would only apply when the decoder is configured as a "Loco" decoder and not a "Switch" decoder, CV121 would need to be set to 1 (or 5 or 9) to allow the A1 output to trigger a servo. CV122 & 123 would then set the arc of travel on the servo. The servo would be at one end when the function is "off" and the other when it is "on".
 
Mark,

Thank you for your prompt reply.
I had sort of figured out the CV stuff, but confirmation is always good, and I have posted the question on the Massoth forum, but no response yet. I'll give it a few days and then email to the address you suggested if I get no response.

Martin
 
As the product you are using has now been discontinued and replaced with a newer product (8156601), I thought I would check to see if Servo operation is possible with it, there is no mention of servo control in the manual for the new product, so it is possible that the old one does not either and the original documentation is wrong.
 
Hi You must use a 5 Volt regulator to give you the 5 volts Plus voltage. CV 122 is adjusted for the low end stop i.e 16 and CV 123 is the top end stop i.e 32 CV 121 is i.e 1 servo with end stops. +4 servo output in reverse. +8 servo is switched off after movement If not a 5 Volt regulator a Massoth 8242050 eMOTION 6 Volt Fixed Voltage Regulator for the servo.
Hope this helps

Alan
 
Hello Alan,

Thank you for an informative reply.
One thing remains; I now assume the two outputs from the decoder would supply the ground connection to the servo, and the PWM 'signal' connection, but which one is which? Difficult to identify the decoder terminals as they are both the same!
Sorry to be so picky but I wouldn't want to endanger either decoder or servo :o

Martin
 
Hi Martin.
I have not got that information I do not think you can hurt the servo or decoder the 1 to 2 ms pulse from the decoder to the servo is 5 volts so if you connect it to the regulator ground it just wont work. I use servos with PIC chips that I Write software for and in the past connected them incorrectly with no damage.
Sorry I can not help you more. Massoth does not give that information either.
Alan.
 
Alan,

Thanks for the reassurance. I'll give things a try when I have some time.
I still have not had a response on the Massoth forum, so I may email direct and ask for some more info. Any extra information I gain I will obviously share here.

Martin
 
Martin,
One more suggestion connect 4 AA battery's to the servo supply i.e. positive and negative then connect the servo white or yellow wire and the battery negative to the decoder. It will not harm the decoder as the servo supply is isolated. One way round it will work the other way it wont, the working way will tell you the negative and the signal on the decoder
Alan
 
Alan,

Thank you once again for your help.
I have today connected a servo as you suggested (but used a 5volt supply) and the servo appears to move to it's stop in one direction only with function key 1, and I cannot make it return.
I have the CVs set as you suggested, but the servo only responds to function key 1, and only in the one direction. It may be that other CVs need tinkering with.

Martin
 
Hi Martin.
For programming the decoder requires an electrical load of 60mAmps. For this you may connect a switch motor to the output terminal of the decoder.
F1 pressed once should send the servo to one end press again and the servo will go to the other end. With the Massoth program on the computer it is easy and is a free download.

Alan
 
Hi Alan,
I'm getting to be a bit of a nuisance here aren't I ::)
I do use the Massoth DCC programming software, and use a lamp as load on the decoder which gives me feedback from the decoder when programming CVs, so that part I know is OK. (on the subject of decoder load when programming, one part of the manual states 60mA load, and a later entry states 100mA - go figure!)
I'm correct I believe in using a loco address, with CV29 set to 2 (28 speed steps), CV121 at 1, and CV122 & 123 at default (16 & 32) as you suggested. Also as you stated, the servo does not work at all when connected in one polarity, and just moves in the one direction when the polarity is reversed (that sounds like a Dr Who statement "reverse the polarity" ;) )
So if I am making bad assumptions, please do tell. I am determined to get this working. I have an idea to use a servo for some level crossing gates/barriers if I can.
Martin
 
Hi Martin,
I cannot see where you are going wrong. To make things easy open Massoth DCC programmer load Massoth DiMAX 1 Channel Switch Decoder. Click on General, leave all settings except "Switch address" set to "loco address" then "A1 special function servo" set it to "RC servo operation with two end stops". then program decoder. That should set it to loco address 3 and try it. When you switch it on the servo will go to one end when you switch it of it will go to the other end. For all my servos I use an 8F. But please come back to me if it doesn't work.

Alan
 
Alan,

Well, I tried what you suggested and I did get some response from the servo. But nothing consistent or predictable. So, I thought it may be the power supply and swapped for 4 x 'C' cells, but still no good. A couple of questions ( :-[ ) - should the voltage output be reduced from it's max, and should the speed steps be changed. I run 28 speed steps, and the default is 14. (I did experiment, to no avail)
You mention that the servos you use are 8F, I'm afraid that doesn't mean much to me. Would you mind enlightening me?
Thanks for your patience Alan.

Martin

[edit] Just wish my trusty 'scope was still alive, so that I could see exactly what comes out of the decoder. I took a look at the Massoth 6V PSU manual, and it mentions a pullup resistor being incorporated in circuit, but doesn't give a value - I guess that would be between servo signal lead and +volts. Any ideas on that score? [/edit]
 
Hi Martin

The 8F I mentioned is the Massoth 8F decoder and it uses a 4.7k ohm pullup resistor to the positive 5volts. Why the 1-2 millisecond pulse needs this I dont know
so I think this is our only option. Like yourself I would use my scope to look at the output of the decoder but I am afraid I cannot help you with this as I am as I am in Portugal until May. I have looked on the Massoth forum and I can see that you have asked for help. Please let me know what happens.

Alan
 
granddad said:
I took a look at the Massoth 6V PSU manual, and it mentions a pullup resistor being incorporated in circuit, but doesn't give a value -
Click to expand...

Page 3............

The pull-up resistor (2) required is already integrated on the eMOTION 6 Volt regulator board.

Page 5.............

Technical Data Pull-up resistors: 2x 3.3 KOhms


CV-Values
CV‘s are usable with loco addresses (L), switch addresses(S) or with both (LS).

51 F1 Special Function 67 LS See attachment 2
52 F2 Special Function 67 LS See attachment 2
121 A1: special function RC servo 0 L 0..13
122 A1: lower limit 16 L 5..50 Must be adjusted to the RC servo
123 A1: upper limit 32 L 5..50 Must be adjusted to the RC Servo

(CV 121) Special function A1

0 no function regular function output
1 RC servo operation with two end positions function off/ function on
+4 RC servo output in reverse
+8 RC servo is switched off after movement


Function Outputs
The function outputs 1+2 (SW1) are coupled. These outputs feature a dual power amplifier to facilitate the operation of switch drives in two directions. Therefore these coupled outputs must never be operated at the same time. An intelligent protection software inhibits the operation in one direction in case the reverse direction output is switched on at the same time. The function outputs are freely programmable in the loco mode. (F-key assignment and direction dependent control).
 
Arthur,
Thank you for your reply - yup! I missed that mention of the 3k3 pullup resistors. Regarding the CVs, I have tinkered with them as I think can be seen from earlier posts. CVs 122 & 123 state 'must be adjusted to the RC Servo' but don't give any clue as to what those settings actually do, or have I missed something else :-\ As I said previously, I just wish I still had a working 'scope. I'm guessing here, but maybe they pertain to the PWM 'spread', so to speak. Any advice would be most welcome.

Alan
Enjoy Portugal, and I shall be persevering here in chilly UK ;)

Martin
 
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