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PIR to Arduino to Transistor and LEDs

eTech

Well-Known Member
Hello eTech, Pommie and the ETO forum,

Been jammed at work and have not had time to make adjustments until today.

Thanks for hanging with me during extended periods between updates..

As mentioned in post #35 have bread boarded the system following fritz marked
'PODACAL 12 Volt Complete 200808' The system works as expected. That is,
when 12v power is applied to the breadboard and the Arduino barrel jack,
simultaneously, the green LED on the Arduino marked 'On' lights and the yellow
LED labeled ' L' lights. and the nine LED module light and the indicator LED lights comes on.
All of these things happen immediately when my hand is waved at the PIR.
The module lights stay on for
about ten seconds and then goes off. The Arduino 'On' light stays on.
After about six seconds the PIR rearms and the cycle can be repeated.
This would be the behavior required to make the Staircase system work.

Altered the PODACAL according to fritz 'PODCAL 12 Volt Complete 200812' also
in post #35.
When 12v power is applied to the breadboard and the Arduino barrel jack,
simultaneously, the green LED on the Arduino marked 'On' lights and the yellow
LED labeled ' L' come on..
The nine LED module lights, after motion at PIR, come on after about a nine second delay.
At first, because there was no motion. the LEDs stayed on for over three minutes
and it was thought that the LEDs were on permanently. But a second movement
caused the LEDs to go off immediately. Then after about twelve seconds the
the lights came on again.

Still trying to get the exact sequence on the 'PODACAL...200812' because the lights
come on in a delayed pattern.

The closest thing to a pattern that can be discerned is the LED module takes about
ten seconds to come on after PIR motion and stays on until a second wave turns
them off. A third wave turns the lights on again after ten seconds and the cycle
is repeating. That is, motion causes the nine LEDs to light after nine or ten second delay
and stay on a second wave st the PIR makes them go off.

Not sure what causes the initial delay or why the second wave causes the LEDs
to extinguish.

Have begun PCB based on 'PODACAL...200812' View attachment 126582
but will probably concentrate on getting the breadboard to work before going back to the PCB.

Thanks.

Allen in Dallas

PS The same Arduino sketch id used in both tests.

Code:
int led = A0;               // the pin that the sensor is attached to
int sensor = 2;         // the pin that the sensor is attached to

void setup() {
  pinMode(led, OUTPUT);
  pinMode(sensor, INPUT);
  Serial.begin(9600);
}

void loop() {
  int sensorval = digitalRead(sensor);
  Serial.println(sensorval);

if (sensorval == HIGH) {
    digitalWrite(led, HIGH);
  }else{
    digitalWrite(led, LOW);
  }

}
yes...it looks like the code needs to be changed. If the sensor value is high, the led should be low..
 

Pommie

Well-Known Member
Most Helpful Member
Assuming you're using the schematic in post #29 then the following is true,
The sensor pin will go low when motion is detected.
The LEDs will be on when the LED pin is high - the TBD inverts the signal.

So your code is doing the following,
Code:
void loop() {
  int sensorval = digitalRead(sensor);
  Serial.println(sensorval);
   
  if(sensorval == HIGH){            //if no motion
    digitalWrite(led, HIGH);        //turn on LEDs
  }else{
    digitalWrite(led, LOW);        //else turn them off
  }
}
Which, I think, is the opposite to what you want.


Mike.
Edit, missed your post.
 
Hello ETech, Pommie and the ETO forum,

Using the breadboard fritz posted in post #35 marked 'PODACAL....200812' the
sketch
Code:
int led = A0;               // the pin that the sensor is attached to
int sensor = 2;         // the pin that the sensor is attached to

void setup() {
  pinMode(led, OUTPUT);
  pinMode(sensor, INPUT);
  Serial.begin(9600);
}

void loop() {
  int sensorval = digitalRead(sensor);
  Serial.println(sensorval);
 
if (sensorval == LOW) {
    digitalWrite(led, LOW);
  }else{
    digitalWrite(led, HIGH);
  }
 
}
was uploaded to the Arduino.

These result have been replicated several times:
1. Power up Arduino and breadboard (where marked '12v+' and 'grnd').
2. Green LED light at Uno marked 'On' comes on and as does the yellow LED labeled 'L'
No other LEDs come on
3. Hand wave at PIR.
4. After 14 seconds the nine LEDs at the LED module come on
5. The nine LEDs stay on until a second hand wave at PIR
6. After ten seconds, with out any other movement, the the LED module lights come on.
7. Another movement causes the LED modules lights to go off.
8. The cycle, beginning at step three can be repeated.

So the system works in the intended manner using fritz in post #35 marked 'PODACAL....200808'
(LED module comes on immediately w motion at PIR and stays on for nine seconds then reams after six seconds
ready for another cycle.)
and the sketch copied at post #38 but does not work as expected using
fritz in post #35 marked 'PODACAL....2008012' and the sketch copied above.

It has been suggested
'This sounds like a bad/loose connection(s) on the breadboard. Maybe something became loose when you made the changes. Check the connections. ' This is always a possibility. Mistakes have been made in the past. However it is humbly offered that:
1. The breadboard has been checked over and over down to the holes in the breadboards and the colors of the wires.
2. Using the same breadboard have gone back and forth between 'PODACAL....200808' and 'PODACAL....200812'
The changes are
2.1 Remove jumper between PC817 collector and 12V+
2.2 Remove R8 4.7k between PC817 emitter and ground and replace w jumper between PC817 and ground
2.3 Place 22k resistor between PC817 collector and jumper to Arduino 5v output
2.4 Connect jumped to Arduino pin 2 to junction of PC817 collector and 22k resistor

This replacement has been done several times always with the same result.

The TBD62003 data sheet was checked.
Link to TBD62003A Data Sheet
On page one it says the max voltage in is .6 v. But on page three it indicates the
'Input voltage -.5 to 30 v'

Pretty sure the reason why we changed to schematic was to reduce the voltage into the
TBD62003A. Is there another DMOS array that would take 12 volts? I looked at TPIC2701
but it looked like its input was very low also.

Is there some way to get the logic at 'PODACAL....200812' to work like 'PODACAL....200808' ?

Thanks.

Allen in Dallas
 

eTech

Well-Known Member
Hello ETech, Pommie and the ETO forum,

Using the breadboard fritz posted in post #35 marked 'PODACAL....200812' the
sketch
Code:
int led = A0;               // the pin that the sensor is attached to
int sensor = 2;         // the pin that the sensor is attached to

void setup() {
  pinMode(led, OUTPUT);
  pinMode(sensor, INPUT);
  Serial.begin(9600);
}

void loop() {
  int sensorval = digitalRead(sensor);
  Serial.println(sensorval);

if (sensorval == LOW) {
    digitalWrite(led, LOW);
  }else{
    digitalWrite(led, HIGH);
  }

}
was uploaded to the Arduino.
The code is still not correct. When the sensor value is "HIGH" (no motion) the LED's should be LOW (off).
Like this:

Code:
if (sensorval == LOW) {
    digitalWrite(led, HIGH);
  }else{
    digitalWrite(led, LOW);
  }
and the sketch copied at post #38 but does not work as expected using
fritz in post #35 marked 'PODACAL....2008012' and the sketch copied above.
Post #29 will work if you fix the code.

It has been suggested
'This sounds like a bad/loose connection(s) on the breadboard. Maybe something became loose when you made the changes. Check the connections. ' This is always a possibility. Mistakes have been made in the past. However it is humbly offered that:
1. The breadboard has been checked over and over down to the holes in the breadboards and the colors of the wires.
2. Using the same breadboard have gone back and forth between 'PODACAL....200808' and 'PODACAL....200812'
The changes are
2.1 Remove jumper between PC817 collector and 12V+
2.2 Remove R8 4.7k between PC817 emitter and ground and replace w jumper between PC817 and ground
2.3 Place 22k resistor between PC817 collector and jumper to Arduino 5v output
2.4 Connect jumped to Arduino pin 2 to junction of PC817 collector and 22k resistor

This replacement has been done several times always with the same result.
Per post #29.
There should be 5v at the collector of PC817 when motion IS NOT detected.
There should be 0v at the collector of PC817 when motion is detected.

2.4 The Arduino pin is marked "5V". There is no pin number. Please recheck.

The TBD62003 data sheet was checked.
Link to TBD62003A Data Sheet
On page one it says the max voltage in is .6 v. But on page three it indicates the
'Input voltage -.5 to 30 v'

Pretty sure the reason why we changed to schematic was to reduce the voltage into the
TBD62003A. Is there another DMOS array that would take 12 volts? I looked at TPIC2701
but it looked like its input was very low also.
No. The schematic was changed because using 12v at the gpio inputs will damage the Arduino.
The GPIO voltage must be restricted to ~5v max. The TBD62003A will work fine.

Is there some way to get the logic at 'PODACAL....200812' to work like 'PODACAL....200808' ?
It will work as posted on #29
 
Last edited:
Hello eTech amd the ETO forum,

Got the PODACAL to work and I'm back on track. Thanks for your guidance.

The last chore left before beginning final test before installation is the PCBs.
There are three boards: the sensor modules, the LED modules and the main board.

The LED modules are pretty simple.
LED_Mod_1_7_200830.jpg
LED_Mod_2_6_200830.jpg

The sensor module is more complex because it has the PIR, the transistor and
the opto coupler.
Sensor_Mod_200822_c.jpg
Please accept a request to eyeball the PCB marked 'PODACAL Sensor Module 200822'.
Pretty sure the connection between the PIR, R13 and R15 are correct but if I could
get an opinion before I send them to the manufacturer it could save a lot of
time and money.

Finally, still in the design phase on the main board. Thinking about an Arduino
shield for the main board and the DMOS array IC,
Arduino_shield_for_TBD620033A_200830.jpg
One thing not liked about the Arduino is the connection to the
pins is a bared wire stuck in a slot. Not very permanent
and pretty squirrely depending on the guage of the wire.
A much better connection that has been deployed successfully
is a fixed terminal block.
It does not require soldering so it easy to troubleshoot
and refactor. But with the screw cranked down on the
wire you can give a good yank and it will hold.

So the challenge is to get the terminal blocks connected
to the PCB and get rows of pins, like those coming out
of the headers, to get a sold connection into the UNO.

The system shown in 'TBD62003a Shield....' copied
above will work. But curious if there might be a better
approach.

Thanks,

Allen In Dallas

PS Will post a YouTube URL when the system is
installed at the staircase.
 

Pommie

Well-Known Member
Most Helpful Member
Can I suggest you post the schematic that you're using as trying to find PODCAL whatever is a nightmare. However, I seem to remember that the IR sensor always outputs 3.3V so I'm wondering why all the extra circuitry - why not connect the sensor directly to the Arduino?

Mike.
Edit, without seeing the schematic, are there 10 LEDs with 3 sets of 3 and one on it's own without a resistor?
 

eTech

Well-Known Member
Can I suggest you post the schematic that you're using as trying to find PODCAL whatever is a nightmare. However, I seem to remember that the IR sensor always outputs 3.3V so I'm wondering why all the extra circuitry - why not connect the sensor directly to the Arduino?
Hi

This question has already been asked.
But anyway, the sensor actually only outputs about 2.0v (closer to 1.95v). So we shifted the level.
Also, there are long wires from the sensor to the arduino (above or below carpet), so we used isolators
for some spike protection.

Mike.
Edit, without seeing the schematic, are there 10 LEDs with 3 sets of 3 and one on it's own without a resistor?
The schematic is on post #29.
 

eTech

Well-Known Member
Hello eTech amd the ETO forum,

Got the PODACAL to work and I'm back on track. Thanks for your guidance.

The last chore left before beginning final test before installation is the PCBs.
There are three boards: the sensor modules, the LED modules and the main board.

The LED modules are pretty simple.
View attachment 126750
View attachment 126745

The sensor module is more complex because it has the PIR, the transistor and
the opto coupler.
View attachment 126747
Please accept a request to eyeball the PCB marked 'PODACAL Sensor Module 200822'.
Pretty sure the connection between the PIR, R13 and R15 are correct but if I could
get an opinion before I send them to the manufacturer it could save a lot of
time and money.
I believe you have too many components on the Sensor Module.
Has there been a new major change?

If you review the schematic post #29, the Sensor module should only have the components shown in the "PIR" block.
You have lumped together both the "Sensor" components and the "Interface" components onto the same board.
If that is the case (and it hasn't been), then there's no point in having the optocouplers. The optocouplers protect the GPIO inputs since the sensors will be some distance away and will be connected with long wires to the arduino GPIO inputs. So the long wires connect the transistor at the remote Sensor(s) to the optocoupler(s) located at the central arduino.
A new "interface module" should contain the components shown in the "Interface" block located at the arduino.
Maybe the "interface" components can be located on the "TBD62003a Shield"? Seem like there might be enough room.
Otherwise, the "interface" module should be a separate module. All eight interface channels could be on the same module.

Finally, still in the design phase on the main board. Thinking about an Arduino
shield for the main board and the DMOS array IC,
View attachment 126748
One thing not liked about the Arduino is the connection to the
pins is a bared wire stuck in a slot. Not very permanent
and pretty squirrely depending on the guage of the wire.
A much better connection that has been deployed successfully
is a fixed terminal block.
It does not require soldering so it easy to troubleshoot
and refactor. But with the screw cranked down on the
wire you can give a good yank and it will hold.

So the challenge is to get the terminal blocks connected
to the PCB and get rows of pins, like those coming out
of the headers, to get a sold connection into the UNO.

The system shown in 'TBD62003a Shield....' copied
above will work. But curious if there might be a better
approach.
Nice...I like the "shield" form factor approach. You should be able to get all the parts.
You'll need to determine what to do about the "Interface" components.

PS Will post a YouTube URL when the system is
installed at the staircase.
Cool...
 
Last edited:
Hello eTech, Pommie and the ETO forum,

Someone had requested a post of the latest schematic so it doesn't have to be looked for twenty posts back.
PODACAL_12v_complete_200812_b.jpg
Edit, without seeing the schematic, are there 10 LEDs with 3 sets of 3 and one on it's own without a resistor?
Actually, the tenth LED w/o a resistor is a fixed terminal block for for power out. Then I realized
power out is not needed. The LED modules are end nodes. So removed one of the fixed terminal blocks
on LED Mods 1 and 7.
LED_Mod_1_7_200903.jpg

The need to place the opto coupler between the sensor module and long wires is now understood.
The eight PC817s are now on the main board which simplified the sensor modules.
Sensor_Mod_200831.jpg
PODACAL_Main_Board_200903.gif
Rather than seat the fixed terminal block (FTB) on top of the headers (which go down into the Arduino)
it was decided to put the FTB for the Arduino input and the DMOS out put on the main board PCB
and create a trace between FTB and the headers.

Lot of work with calipers and the measure function of Dip Trace (PCB software)
to ensure that the header coming thru the PCB line up with inputs on the Uno.

Will eyeball the PCBs for a couple of days and send them off to PCB manufacturer.

After that it is some 3D printer work and deployment.

Will advise.

Allen in Dallas
 

eTech

Well-Known Member
Hello eTech, Pommie and the ETO forum,

Someone had requested a post of the latest schematic so it doesn't have to be looked for twenty posts back.
View attachment 126818
o_OModules 1-6 used to be 12 LEDs each. Module 7 was 18 LEDs.
Did you intentionally change the number of LEDs per module?

BTW- the current draw will be different if you've changed the LED groupings.
Your modification to the LED's on the schematic is wrong.

Actually, the tenth LED w/o a resistor is a fixed terminal block for for power out. Then I realized
power out is not needed. The LED modules are end nodes. So removed one of the fixed terminal blocks
on LED Mods 1 and 7.
View attachment 126820
:eek:Where are the current limiting resistors?
The LEDs and/or DMOS chip will burn up without them.
 
Hello eTech and the ETO forum,

Did not realize that the current draw to the LED modules was critical.
Think may have strayed from the schematic in post #29 which is what
the bread board proof is based upon.
This is minor redraw of post 29 but I think it is electrically the same .
It shows the relationship between the LED mods in the schematic and
the design in Staircase Application PIR to Arduino to LEDs copied below.

PODACAL_12v_complete_200907.jpg
Then went back and compared POCADAL 200812 etl/acp to the original design
staircase_design_200528_600_x_400.gif
and it lines up now.

So the LED module were refactored. The PCB image from Dip Trace is shown
and then a white background image of the PCB is shown because it is
easier to read. Three of these modules are daisy chained for group LM7 and LM1
and two are chained for LED groups LM2 thru LM6.
LED_Mod_1_7_200907.jpg

LED_Mod_1_7_200907_w_components.jpg

The only change from POCADAL 200812 etl/acp to the Main Board PCB is
schematic shows seven PIR sensors and the Main Board has eight PIRs.
But the eight PIR takes another slot on the Arduino without effecting the
rest of the system.

BTW- the current draw will be different if you've changed the LED groupings.
IN POCADAL 200812 etl/acp one LED module has twelve LEDs and the other has
eighteen. So the DMOS pins will ground any number of LEDs between twelve
and eighteen?

Thanks.

Allen in Dallas
 

eTech

Well-Known Member
So the LED module were refactored. The PCB image from Dip Trace is shown
and then a white background image of the PCB is shown because it is
easier to read. Three of these modules are daisy chained for group LM7 and LM1
and two are chained for LED groups LM2 thru LM6.
View attachment 126872

View attachment 126873
You should spend some time cleaning up the traces on this PCB module.
-or-
The cost difference between a 1 and 2 layer board is small these days. If you make this a two layer board, you can use the bottom layer for the -LED supply plane and use the top layer for +LED supply and the remaining signal tracks.

In addition, make all (track) junction connections at the component PAD locations (no more than two tracks connections), and keep all components at 0 or 90 degree orientation. Your board will look much cleaner.

Each limiting resistor can be 1/4 watt for each 3-LED string that draws 20mA current and a 12v supply.
What type of LED are you using? Part number?

The only change from POCADAL 200812 etl/acp to the Main Board PCB is
schematic shows seven PIR sensors and the Main Board has eight PIRs.
But the eight PIR takes another slot on the Arduino without effecting the
rest of the system.
Ok...but i don't see the eighth one. Where is it?

IN POCADAL 200812 etl/acp one LED module has twelve LEDs and the other has
eighteen. So the DMOS pins will ground any number of LEDs between twelve
and eighteen?
This statement is confusing.
Each output pin of the DMOS chip can handle at least 240mA. The datasheet says 500mA, but that would require a heat sink, so I'd want to operate well below this. Each LED module, the way you've configured it, will draw 40mA (20mA per 3-LED string). So, if you do the math:

1 module = (2ea 3-LED strings) = [email protected] total
240mA/40mA = 6 modules (equivalent to 12ea 3-LED strings) Max each DMOS output pin.

"eighteen. So the DMOS pins will ground any number of LEDs between twelve
and eighteen?"
You really shouldn't use the name "LEDs" in this question because is misleads. You are connecting "LED modules" to the DMOS outputs. The modules present quite a different load than discrete LEDs.
 
Last edited:
Hello eTech and the ETO forum,

1.
'In addition, make all (track) junction connections at the component PAD locations (no more than two tracks connections),
and keep all components at 0 or 90 degree orientation. Your board will look much cleaner.'
Looked at doing the LED modules, the sensors modules and especially the most complex of the three, the Main board, in
multi layer PCBs. (A year ago about 300 bucks were ponied up for the four layer version of Dip Trace
which was very helpful in doing a very complex board.) But could not discover how reworking any of the boards
would save enough space to warrant reworking them.

Refactored the LED module making no than two connections per pad and approaching at ninety degrees.

LED_Mod_1_7_200910.jpg

2. The LEDs are from Tayda Electronics
Emitting color: Green
Diameter: 5mm
Lens color: Water Clear
Forward voltage(V): 3.2-3.4
Current(mA): 20
(This means the diode draws 20 mA plus or minus all the time or the diode draws 20 mA maximum?}

3. 'Ok...but i don't see the eighth one. Where is it?'

The eighth sensor does not show on the schematic. But on the Main Board PCB, in post # 49,
pins 10 thru 3 (eight pins) are used as inputs from the sensors.
These are fed by eight fixed terminal blocks marked 'PIR Out' and PIR Rtn' at the six o'clock side of the
Main Board PCB.

(Another change from the #49 schematic is that there are output pins are A0 thru A5, six pins.
But seven pins are required so pin 2 from the opposite
side of the Uno is employed.)


4. Thanks for the math. A knowledge of Ohm's Law and calculating voltage, amperage and resistance was
gained some years ago at the local junior college but its not something I do regularly. So you sort of blew by
me with
1 module = (2ea 3-LED strings) = [email protected] total
240mA/40mA = 6 modules (equivalent to 12ea 3-LED strings) Max each DMOS output pin.
We agree that each LED module has six lights.

And the modules are grouped together in twins (2-6) and triplets (1 & 7)

It is agreed that calling them LEDs is inaccurate. Perhaps the assembly
of six LEDs are called modules and the assembly of two or three
modules are called groups.

So if, as the specs say, esch LED
draws 20mA, would not each module draw 6 x 20 mA or 120 mA?

And groups 1 and 7, as shown on the schematic,
have three modules of six, or eighteen LEDS: 18 x 20 mA = 360 mA
(still well less than the 500mA max set by the TBD62003A)
And groups 2 thru 6 have two modules of six, or twelve LEDs:
12 x 20 mA or 240 mA for those five groups.

Does that make sense?

I guess the main thing is the schematic as shown in post #51 is enough like the schematic in
post #49 to work.

Thanks for your patience and tenacity.

Allen Pitts, Dallas Texas
 

ChrisP58

Well-Known Member
Most Helpful Member
Unfortunately, the link to your LED doesn't have a datasheet (that I could see) so we have to guestimate what the 20mA current refers to. It's most likely the nominal current. And the current at which the brightness numbers are measured. Max could be higher, but we don't know without the manufacturers data. There is no real minimum current, but the brightness falls with current, so there will be a point at which it becomes useless.

It is up to you to limit the current. That's what the series resistance is for. In your case you have three LEDs in series. The same 20mA goes through all three of them, but the forward voltage adds.

The resistor value is the (operating voltage) minus (the sum of all three forward voltages) divided by the current you want. (12) - (3.3*3) / 20mA = 105 ohms. The total current for one 2*3 module will be 40mA.
 

eTech

Well-Known Member
Hello eTech and the ETO forum,

1.

Looked at doing the LED modules, the sensors modules and especially the most complex of the three, the Main board, in
multi layer PCBs. (A year ago about 300 bucks were ponied up for the four layer version of Dip Trace
which was very helpful in doing a very complex board.) But could not discover how reworking any of the boards
would save enough space to warrant reworking them.

Refactored the LED module making no than two connections per pad and approaching at ninety degrees.

View attachment 126913
That's a little better.

2. The LEDs are from Tayda Electronics
Emitting color: Green
Diameter: 5mm
Lens color: Water Clear
Forward voltage(V): 3.2-3.4
Current(mA): 20
(This means the diode draws 20 mA plus or minus all the time or the diode draws 20 mA maximum?}
This is usually the spec'd rated forward current (20ma) at the rated forward voltage (somewhere between 3.2v and 3.4v) across the LED. The LED is basically a diode that conducts in one direction. If used without a current limiting resistor, the LED will continue to increase conduction (drawing more and more current) until it burns up (and a puff of magic smoke appears). That's why its important to have a current limiting resistor, or some other means, to set a finite limit of current thru the LED(s). So...basically...the LED's maximum current draw is the point where it open circuits because its light emitting surface burned up.

3. 'Ok...but i don't see the eighth one. Where is it?'

The eighth sensor does not show on the schematic. But on the Main Board PCB, in post # 49,
pins 10 thru 3 (eight pins) are used as inputs from the sensors.
These are fed by eight fixed terminal blocks marked 'PIR Out' and PIR Rtn' at the six o'clock side of the
Main Board PCB.

(Another change from the #49 schematic is that there are output pins are A0 thru A5, six pins.
But seven pins are required so pin 2 from the opposite
side of the Uno is employed.)
Ok.

4. Thanks for the math. A knowledge of Ohm's Law and calculating voltage, amperage and resistance was
gained some years ago at the local junior college but its not something I do regularly. So you sort of blew by
me with

We agree that each LED module has six lights.
No. Five LED modules have two series connected strings of LEDs. And two LED modules have three series connected strings of LEDs.

And the modules are grouped together in twins (2-6) and triplets (1 & 7)

It is agreed that calling them LEDs is inaccurate. Perhaps the assembly
of six LEDs are called modules and the assembly of two or three
modules are called groups.
Here's my take on this:
Module x1 contains 1 set of LEDs (if there was one)
Module x2 contains 2 sets of LEDs (Used at "intermediate" stair-step locations)
Module x3 contains 3 sets of LEDs (Used at "begin/end" stair-step locations)

So if, as the specs say, esch LED
draws 20mA, would not each module draw 6 x 20 mA or 120 mA?

And groups 1 and 7, as shown on the schematic,
have three modules of six, or eighteen LEDS: 18 x 20 mA = 360 mA
(still well less than the 500mA max set by the TBD62003A)
And groups 2 thru 6 have two modules of six, or twelve LEDs:
12 x 20 mA or 240 mA for those five groups.

Does that make sense?
Your thinking would be almost correct if all the LED's were connected in parallel. But they are not.
Since each string of three LED's and its limit resistor is connected in series, the same amount of current (20mA) flows through the entire string. The reason we can connect them this way is because we are using a 12v supply to account for the multiple voltage drops across the LEDs and limit resistor. Therefore, each string of LEDs draws 20mA of total current.

I guess the main thing is the schematic as shown in post #51 is enough like the schematic in
post #49 to work.

Thanks for your patience and tenacity.

Allen Pitts, Dallas Texas
Kinda tired....I'll have a look and get back to you..
 
Last edited:
Hello ETO forum,

Thanks to Pommie, ChrisP58 and especially eTech for providing excellent adult supervision through 55 posts in this thread.
(What's the record for the longest thread?) I believe we have a good working system.

The PCBs have been sent off to Osh Park, the PCB manufacturer, and are scheduled to come back to me in Dallas on
Wed., Sept 23. The following Saturday will be spent on construction and assembly.

This may be a good place to make this my last post to this thread and open a new thread on assembly and testing of
the Staircase system when the assembly is complete . Until then I remain

Yours gratefully,

Allen Pitts
Dallas Texas
 

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