Railroadguy
- Mar 31, 2014
- 5
- Joined
- Mar 31, 2014
- Messages
- 5
Greetings all-
First post so be gentle ;o)
Back when I was growing up, I used to tinker a lot with electronics and became pretty good at designing simple circuits. Then I went to college where they confused the crap out of me with Ebers-Moll propaganda and the like. As a railroad/transit signal and train control engineer, I deal more at the application level with respect to design and thus, my understanding of electronics has become pretty rusty.
I have built a conveyor model that I intend on using to demonstrate automation controllers and general automation concepts to 5th grade elementary students. The model uses a color sensor to detect the color of like-objects as they pass the device. Then the objects are pushed off the conveyor by diverter gates where they land in one of three classification bins (sorted by color). I had considered using soleniods to control the gates but found that they tended to be too forceful in their movement and instead decided to use servos that are typically used for radio-controlled cars, boats, planes, etc.
Servos typically respond to a pulse whose period/width is varied between 1-2msec which in turn translates to a rotation of 0-90 degrees respectively. Attached is a copy of the circuit which is based on an NE555 timer. Under "normal" or non-operating conditions, contact CR1 is open and the output of the timer is a pulse train with an on-duration of 2ms. When the relay contact is closed (based on an output of a PLC), it shunts the series-combination of 5K pot and 5.6K resistor and the output pulse changes in duration to about 1ms causing the servo to turn 90 degrees.
I was concerned about using relays and my intuition was correct as there is a minor problem with this arrangement: Contact-bounce. In addition, the relays that I am using (simple industrial control model) have 24V coils which are being operated at 12V which doesn't help the situation (The conveyor motor can only run on 12VDC and I didn't want to have two different supplies for the model. This may qualify me as being lazy!).
Does anyone have any advice, ideas, thoughts, suggestions or the like regarding how I might remedy this problem? To be honest, the "chatter" that I am experiencing is not too bad but let's just say that, 1. It bothers me, and, 2. I'm sure that there is a better way which would avoid the issue, and of course, 3. I really don't want to have to explain contact-bounce to some smart-alec 5th grader who will find that more intriquing than the model itself!
Thanks in advance!
Jim
First post so be gentle ;o)
Back when I was growing up, I used to tinker a lot with electronics and became pretty good at designing simple circuits. Then I went to college where they confused the crap out of me with Ebers-Moll propaganda and the like. As a railroad/transit signal and train control engineer, I deal more at the application level with respect to design and thus, my understanding of electronics has become pretty rusty.
I have built a conveyor model that I intend on using to demonstrate automation controllers and general automation concepts to 5th grade elementary students. The model uses a color sensor to detect the color of like-objects as they pass the device. Then the objects are pushed off the conveyor by diverter gates where they land in one of three classification bins (sorted by color). I had considered using soleniods to control the gates but found that they tended to be too forceful in their movement and instead decided to use servos that are typically used for radio-controlled cars, boats, planes, etc.
Servos typically respond to a pulse whose period/width is varied between 1-2msec which in turn translates to a rotation of 0-90 degrees respectively. Attached is a copy of the circuit which is based on an NE555 timer. Under "normal" or non-operating conditions, contact CR1 is open and the output of the timer is a pulse train with an on-duration of 2ms. When the relay contact is closed (based on an output of a PLC), it shunts the series-combination of 5K pot and 5.6K resistor and the output pulse changes in duration to about 1ms causing the servo to turn 90 degrees.
I was concerned about using relays and my intuition was correct as there is a minor problem with this arrangement: Contact-bounce. In addition, the relays that I am using (simple industrial control model) have 24V coils which are being operated at 12V which doesn't help the situation (The conveyor motor can only run on 12VDC and I didn't want to have two different supplies for the model. This may qualify me as being lazy!).
Does anyone have any advice, ideas, thoughts, suggestions or the like regarding how I might remedy this problem? To be honest, the "chatter" that I am experiencing is not too bad but let's just say that, 1. It bothers me, and, 2. I'm sure that there is a better way which would avoid the issue, and of course, 3. I really don't want to have to explain contact-bounce to some smart-alec 5th grader who will find that more intriquing than the model itself!
Thanks in advance!
Jim