Light activated label dispenser

Thread Starter

gerstley

Joined Nov 20, 2015
58
Hi Bernard. I built the circuit using 300 ohms at R6 and 10k at R3,R4.The motor runs but there are some problems I can't seem to figure out. At powerup the motor runs but the photo transistor seems to have no effect. I played with R1 (the variable resistor) but nothing would get the motor to stop. Shorting across the transistor leads stops the motor. After doing that, pressing SW1 starts the motor up again but pressing it a second time does not stop it. Any thoughts?
 

Bernard

Joined Aug 7, 2008
5,612
With just label backing over Q1, measure V at pin 6, vary R1 to see range of Vs. Needs to go over 8V.
Motor not stopping. Opaque paper over Q1, measure V at Q3-9, press SW1, after 3 sec press SW1 again, note V readings.
With motor not running, short Q1 if necessary, Q3-9 should be lo., Q2-1 should be hi
Motor on. Q3-9 should be hi after about 1/2 sec., Q2-1 is lo.?
 

Bernard

Joined Aug 7, 2008
5,612
Now I know why: You have two IR LED's, should have 372737, IR LED & 2120410, IR transistor. Confusion came from post # 26
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
I am using the 372737 LED and the Jameco #112176 photo transistor. I also have the #1950825 LED which I also tried with the transistor but that did not work either.
 

Bernard

Joined Aug 7, 2008
5,612
The 112176 is really long wave-- 9999nm, maybe too far for 372737 @ 880 nm? Are you sure none are reversed? Cathode of LED is usually the short lead & flat edge is emitter on transistor. Measure V across the IR LED, should be about 1.5V.
 
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Thread Starter

gerstley

Joined Nov 20, 2015
58
I have 1.15V across the LED. I am sure I have the polarity of the 2 correct. I have spent a lot of time studying it trying to figure out what is wrong.
 

Bernard

Joined Aug 7, 2008
5,612
You were right in checking further. I do not have an answer other than bad part. No time today. Party prep. at VA Hospital.
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
Another update. I apparently had a bad photo transistor. I put in a new one and the circuit works! Two problems remain. First, the button starts the motor but it does not stop it. Only light on the photo transistor stops the motor. Second, the motor speed control does not work properly. The motor only runs on high speed. When the motor ground is connected directly to the speed control I am able to vary the speed but when the ground goes through the MOSFET the speed control doesn't function.
Getting closer. Thanks for sticking with me on this.
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
With just label backing over Q1, measure V at pin 6, vary R1 to see range of Vs. Needs to go over 8V
The new photo transistor is working so the motor stops with just the backing (0 V at pin6).
With motor not running, short Q1 if necessary, Q3-9 should be lo., Q2-1 should be hi
Q3-9 reads 0 V. Q2-1 reads 12.3V.
Motor on. Q3-9 should be hi after about 1/2 sec., Q2-1 is lo.?
Q3-9 voltages rises to 11.5 V over about 2 seconds and then drops and repeats. Q2-1 reads 0V.

Also;
Last thoughts before I break it down & file it away: I put it on a breadboard using a LED to monitor output. Worked at power up.
As SW1 will be separated from circuit by maybe a foot, thought it adviseable to lower impedance of SW1 pulse by changing R6, 10k down to
300 ohms, +_ 20%. Same for R3-R4, might go as low as 10K if gap can still be detected. Use twisted pair for both SW1 & Q1
I am using a foot operated switch, so the switch is on a 6 foot stranded wire lead. Not sure if that matters.
 

Bernard

Joined Aug 7, 2008
5,612
Is the motor running while measuring V at Q3-9 ? It should not be oscillating with motor running.
Re check values of R7 & C2, the 2 sec seems too long. is still jumping up and down, start with motor off and start with SW1 and keep SW closed & remeasure. Any change ?
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
It seems the voltage at Q3-9 is not oscillating after all. It may have just been bad contact by the person holding the tester lead. I have scolded them. The voltage rises to 11.3 volts but it took 7 seconds. We had the same result when holding the SW1 closed. R7 measures 99K ohms. My multimeter doesn't measure capacitance. It should be 10mf.

Also, would I use an automotive type 12V 5 pin relay for the relay?
 

Bernard

Joined Aug 7, 2008
5,612
7 sec. is just too long; either reduce R7 to 10k or C2 to 1 uF or do both.
An automotive type relay should be fine. Single pole- single throw or SPDT, or DPDT OK.
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
I dropped R7 to 10k and used a 0.1 uf for C2. Pin 9 came up to 11.5V in a half second but the switch still does not stop the motor. When I take the wire off pin 10 and short it to ground the motor stops so the reset seems to work.
For the motor speed control, would it work to turn the speed control on and off with the MOSFET as shown on my sketch? The motor speed control should work properly with the motor + and - connected directly to it.
Scan_20151222.jpg
 

Bernard

Joined Aug 7, 2008
5,612
I think your sketch should work.
Maybe we need to add a RC delay between Q4-4 & Q2-1 with same values as R7 & C2. With motor on
Q2-1 is lo, Q3-9 is hi, but when SW1 closes Q2-1 goes hi within nano sec.s. so for about 30 us both Q2-1,2 & Q3-9,8 are all hi so we might have both a reset & set so if set wins motor keeps running.
 

Thread Starter

gerstley

Joined Nov 20, 2015
58
That fixed it! The switch starts and stops the motor now and the speed control also works. Just a couple other questions if I can. Do I still need a diode at the motor with this new setup or does the motor control cover that for me? Also, if the label stops with the sensor in the gap, the switch wont start the motor. Is there a simple way to make sure the motor runs for a fraction of a second after seeing the gap so the sensor is looking through a label when the switch is pressed to start the motor? Or else, (preferably) can the switch be set up to start the motor regardless of what the sensor is seeing (light or dark).
 

Bernard

Joined Aug 7, 2008
5,612
Replace the lead from Q1 emitter to junction of R3 & R4 with a .1, C6 ( or any thing close ).
Add R9 from emitter to ground, around 100K . Should give about a 10 ms pulse to reset Q6 which is then ready for a SW1 start .
If you ever get down to the city, say Hi to my old school PS 14, Staten Island, 1937-1940.
 
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