3 aspect model RR signalling help plse

Status
Not open for further replies.
I think I'm gonna go with the 4 diodes thing. I understand that. Still not sure where the volts lost comes from tho'. I thought a diode just let current go in one direction, didn't know it used voltage to make it work like a motor.

I've got three signal block circuits working now. So tomorrow I'm off to get the bits to complete one detector of each circuit type. Then once they're built I can test them and see how much smoke I get or how slow the loco is.

While there is no rush for this, with the roadbed still being laid, I would like to get an idea of what I'm dealing with when it comes to building each one.
 

OK, good luck.

A silicon diode does not have zero resistance when conducting. One can say that its resistance when conducting adjust itself so that there is always about a 0.7 volts drop no matter what the current. According to Bill it's atomic science (try Fermi).

Because all of the current is going through the power transistors that version (no diodes) is very sensitive. (Refer to the two wet finger picture). It's probably the cheapest version too. I suggest you try that first. You are not going to blow your DCC booster. It has a fast cct breaker and the Twin-T is in series with the booster/track circuit. So you are quite safe.

If you want to try the signal transistor option I suggest that you try the two back to back 3 amp diodes across the base emitter junctions first. It will probably work fine. Then you can save the other two diodes for the next detector.

I'd like for you to confirm that the photo-isolator requires 10 Ma to operate. I think I got that from somewhere.

Good luck with the construction.
 
You have quite a range of input current here. The absolute Maximun input current s 50Ma. the lowest is half a Ma. I think that the circuit I sent you where the colector resistor is 3.9K should work OM at 3 Ma. But try lowering this resistor to 2.4 K ohms. That gives it a bit more OOmph. (5 Ma)
 
I just checked Maplin for cost on three options
2 BD442 = .65 each
2 = 2n2222 .19-.22 each
bridge rectifier .27 or more depending on which one or single diodes are .16 (1n4001)
couldn't find 1n4148. need to look again as they are more common.
The 2 transistor less diodes works but MO connecting 18v AC to transistors???
May be perfectly alright, just doesn't sound right.
 

I take it that you are located in GB. Maplin is the UKs equivalent to Radio Shack. Did you make a typo. 2 = BD441s not 442s. I received a msg fro Angie that the 441s are the NPN equivalent to the 442s. The 2N2222 should probably not be produced anymore because they were leaky. They should be 2N2222A. I dont know if Angie prefers NPN or PNP. If its NPN then it should be the BD441/2N2222A transistor combination. If its PNP then it's the BD442/2N3906 combination. The cost should be the same.

Don't connect 18 volts to the 2N2222s without the shunting diodes across them. And then try only one back to back pair. Do try the power transistor version first. It is much more sensitive. Look at my pictures and diagrams too. You will note that the 18v DC (Twin T supply) only has one connection to the circuit and that is to an LED with a 3.9K ohm resistor. It won't smoke. The Power tansistors won't smoke either because the are in series with the track load. Put a 2K resistor across the track to start with, apply DCC and watch the LED light up. Then keep reducing the resistor value down to 10 ohms, all the while feeling and checking how hot the power transistors get. With DCC they shouldn't even get warm. Angie is also using a 12v Twin-T supply (I think). That photo-isolator needs a min of 5Ma to work. At that (lower) voltage 3.9K may be a bit high. But try it anyway with a cheapy red LED and resistor first ( like my lash up ). The visual feedback will indicate that the detector works. Then I suggest a 2K resistor be exchanged for the 3.9K one. It is still a bit close to that data sheet minimum. The Maximum is 50Ma. So you have lots of wiggle space.

The value of the collector resistor affects the sensitivity of the circuit. The lower, the less sensitive. So we should keep it as high as possible. If 2 K works I suggest we stay with that.
 
Last edited:
You guys are comparing apples and oranges. The BD441 is a big TO126 transistor that can handle 4A and the 2n2222 is a little TO92 transistor that can handle 1A.

Mike.
 
Pommie said:
You guys are comparing apples and oranges. The BD441 is a big TO126 transistor that can handle 4A and the 2n2222 is a little TO92 transistor that can handle 1A.
Click to expand...

And herein lies my problem. I have the circuits working in a simulator but without specifying what each component is, except the resistors.

I have no idea where to measure current or volts to know which component I require, with regard what it can 'handle'. I have no idea why a diode uses 0.7V when it's not a motor! These are things I'd like to know so I am not simply having others put up a schematic that works and I follow blincly. I have a need to learn and know why things happen. I grasp the concept of LED's needing a resistor and I know how an NPN transistor works, but that's about it, oh, and I know how a battery works

[Added]
I got the TIP31C, 3A transistor in P3c case style.
collector-emitter: 100V
collector-base: 100V
emitter-base: 5V
continuous peak current (collector): 3A
base current: 1A
collector cutoff: 0.3mA
emitter cutoff: 1mA
current gain: 10 to 50
collector-emitter saturation : 1.2V
base-emitter on: 1.8V

And I know I don't understand a word of what I just typed
 
Last edited:
I am in Salmon, Idaho = the states
The diodes can be had for as little as 3 cents each, The 2n2222a transistors can be found very cheap as well.
Don't know what shipping costs are or dollar conversion.
IMO using the small signal transistors would be cheaper and a smaller board per circuit.
 
I usually go to Rapid | Distributors of electronic components, electrical products and educational supplies or Welcome to rswww.com when buying bulk. But Maplin for one or two at a time for testing purposes if I don't have what I need.

Already got 180 x 1N4148 but they're signal diodes not rectifiers. Got four 1N5404's for the rectifier part, two optocouplers and the power transistors, so that's enough for the Twin-T circuit.

Also have 2N3904 npn transistors to complete the other circuit. I think that's all I needed?
 
Pommie said:
You guys are comparing apples and oranges. The BD441 is a big TO126 transistor that can handle 4A and the 2n2222 is a little TO92 transistor that can handle 1A.

Mike.
Click to expand...
Hey Mike, Welcome. I thought the BD 441 was the NPN equiv to the PNP BD442 I'm using. I should have checked that one out.

To fill you in. We are attempting to construct a current sensor device that works in a range from the Ma to the 2 to 3 Amp range. Linn Wescott invented the twin-T circuit in 1958. It is simple two transistor device with their bases and emitters cross coupled. Linn Wescott used power resistors, howver it is possible to use signal transistors by shunting most of the current past these junctions via the use of silicon rectifier diodes. We have found that "modern" forms of this device uses op-amps and is component rich. So the options we are weighing is the signal transisor version using 2N2222As with diverting rectifiers (Diodes) or just a plain pair of power transistors without any diodes. Hence the BD442 and 441 issue.

You are most welcome to join in.

Pete
 
One question before I connect these up.

This is AC and DC working together.

The 12VDC negative s connected to the 16VAC circuit.

I'm a little concerned that the DC will blow the AC or vice versa. Is this possible?
 
angie1199 said:
One question before I connect these up.

This is AC and DC working together.

The 12VDC negative s connected to the 16VAC circuit.

I'm a little concerned that the DC will blow the AC or vice versa. Is this possible?
Click to expand...

Hi Angie,

Both AC and DC are on their own and have their own current path. They are just being "referenced" at a single point so that they can 'see' each other. Besides the DC is limited to less than 20Ma. My lash up didn't smoke and is still working. Plug the circuit in. If you made a mistake and built in a short the DCC booster's safety breaker will trip. As long as the photo-isolator and the 2K (or 3.9K) is the only connection to the Twin-T power supply then the maximum current is far to low to burn anything. Check your wiring and them try it.

P
 
Headlines

A large cloud of black smoke was seen today rising above a province in the UK.
Authorities are trying o locate the ource of the smoke.
At the same instant the smoke was spotted all the electrical power in the UK went out briefly.
An emergency session of Parliment was called for this emergency.
We will keep you updated as the source of the smoke is under investigation.
Film at 11
 
angie1199 said:
One question before I connect these up.

This is AC and DC working together.

The 12VDC negative s connected to the 16VAC circuit.

I'm a little concerned that the DC will blow the AC or vice versa. Is this possible?
Click to expand...

Hi Angie,

Have not heard from you. MrDeb put a panic type message on the board mentioning smoke. I hope he is joking. If you did smoke the circuit then there is a glitch in the construction. (solder bridge -- mistaken transistor pins ---wrong resistor values in the collector circuits ???)
 
It was a joke
Am sure (hopefully) Angi is all right.
haven't herd from her either.
Perhaps we need to send out a search party?
 
MrDEB said:
It was a joke
Am sure (hopefully) Angi is all right.
haven't herd from her either.
Perhaps we need to send out a search party?
Click to expand...

I was a bit worried there. I'm also confused. Angie mentioned getting power transistors AND rectfiers AND signal diodes. I guess the signal diodes are for the LED drivers.

P.
 
Ok guys,

I'm still here. Had a little problem. Thought my dcc power supply had blown up (before making the circuit). So ordered a new one only to find the 2pin adapter for the power supply didn't have a fuse in it!. Now I got 2 power supplies

V funny MrDeb, no smoke as yet. Still sorting getting a test track working. Think it's ok now.

Read both your comments. Now I got 2 questions about them.

1. Pete, if I use NPN power transistors do they get wired up the same as the PNP ones or do I have to change something.

2. MrDeb, are the diodes in the other detector circuit also powr diodes? I got four of them. Is that right?

Now you're both worrying me. Hope I got the right bits!

4 x 1N5402 diodes
2 x TIP31C
2 x Photocoupler thingies
1 x 0.1uF poly cap

will try 2 1N5402's with capacitor and the 2 TIP31C's

Then try 4 1N5402's as rectifier with 2 2N3904 transistors, or does the other circuit also need power transistors?
 
Status
Not open for further replies.

Similar threads

J
  • Question
I need the .lib or .sub extension that contains the LTSPICE model for the 4N35.
Replies
3
Views
2K
crutschow
B
Rodine NCI-12R parts help
Replies
0
Views
656
bluejeans
B
N
  • Question
Need Help Finding this Mic
Replies
17
Views
1K
ZipZapOuch
N
  • Question
Need Help Finding a Part
Replies
2
Views
784
NBD925
N
T
  • Question
Need help with RS232 wiring
Replies
18
Views
2K
For The Popcorn
F
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…