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by lawsonkeith
Sun Apr 28, 2019 7:04 am
Forum: Automation, sensing and robotics
Topic: PLC and Raspberry PI 3 B
Replies: 8
Views: 985

Re: PLC and Raspberry PI 3 B

Hi For data exchange you could use an OPC server which would be the most obvious way of doing it. Failing that Modbus TCP/IP can be used as well but it's really a fieldbus protocol so not ideal. They'd be the obvious generic SCADA and fieldbus protocols I'd look at. I'd avoid vnc and try and do any ...
by lawsonkeith
Fri Apr 05, 2019 8:34 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1655

Re: How best to control higher voltage relays with 12v/24v coils?

Hi 1. I don't think you need optocuplers what are you protecting the PI from? the relay is already a form of isolation. If you are dead set on them the el cheapo relay boards already have them fitted. Optos are generally best avoided. I wouldn't recommend cheap relays either. 2. The ULN2003/2803 is ...
by lawsonkeith
Mon Apr 01, 2019 5:46 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1655

Re: How best to control higher voltage relays with 12v/24v coils?

We used some of the cheap relays where I work - they failed within 2 wks. When you read the product reviews a few people complained about the same issue and the same time frame. I think you get what you pay for really with relays. If it's powering 6A I'd pay the extra money and get something you kno...
by lawsonkeith
Sun Mar 31, 2019 3:06 pm
Forum: Automation, sensing and robotics
Topic: Sound Sensor to catch a specific noise a saw motor gives off?
Replies: 13
Views: 933

Re: Sound Sensor to catch a specific noise a saw motor gives off?

I'd look at the AC current to the motor, if it;s about to stall the current would go up. It;s a lot easier to monitor than a specific audio frequency.
by lawsonkeith
Sun Mar 31, 2019 3:06 pm
Forum: Automation, sensing and robotics
Topic: Sound Sensor to catch a specific noise a saw motor gives off?
Replies: 13
Views: 933

Re: Sound Sensor to catch a specific noise a saw motor gives off?

I'd look at the AC current to the motor, if it;s about to stall the current would go up. It;s a lot easier to monitor than a specific audio frequency.
by lawsonkeith
Sun Mar 31, 2019 2:44 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1655

Re: How best to control higher voltage relays with 12v/24v coils?

Hi No that's not what I meant. So it's a 5-6A load and most budget relays state a 10A contact rating at 250VAC - problem sorted? If in the future he wants to add another load i.e 10-12A in total then add another relay to supply the other load then the contact ratings aren't exceeded per contact. i.e...
by lawsonkeith
Sun Mar 31, 2019 12:41 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1655

Re: How best to control higher voltage relays with 12v/24v coils?

Hi Why not but a relay module from ebay? They are usually optically isolated so can be run off the PI GPIO, you can use those relays direct (240V/10A contact rating) or parallel them up (10A x n) or use them to switch a more powerful relay (if you're turning on a huge load). If you get a 5V model yo...
by lawsonkeith
Thu Mar 28, 2019 2:19 pm
Forum: Automation, sensing and robotics
Topic: Current and Voltage sensors, what are the options?
Replies: 7
Views: 3608

Re: Current and Voltage sensors, what are the options?

You'll need a custom PCB, the current can be done with a hall effect sensor, the voltage would require a isolation amplifier with step down input stage - you can look at how a DVM works to implement this.
by lawsonkeith
Thu Mar 28, 2019 2:05 pm
Forum: Automation, sensing and robotics
Topic: can i switch 24V valves with drv8825?
Replies: 7
Views: 947

Re: can i switch 24V valves with drv8825?

Hi

I was looking at developing a product to do PWM of solenoids using a PI, did you manage to come up with a good solution for it in the end?
by lawsonkeith
Thu Mar 28, 2019 2:00 pm
Forum: Automation, sensing and robotics
Topic: Proportional valves and Raspberry Pi
Replies: 2
Views: 263

Re: Proportional valves and Raspberry Pi

Hi That valves a 4-20mA or 0-10V signal control. You could make a voltage amplifier for you PI that converts the GPIO to a higher voltage (10 or 24) level to do that using transistors, you'd also need a software PWM implementation running on the PI to generate the varying voltage in the first place....
by lawsonkeith
Mon Jun 30, 2014 8:17 pm
Forum: Other projects
Topic: Rasberry Pi RC Car + Camera??
Replies: 10
Views: 22816

Re: Rasberry Pi RC Car + Camera??

Hi

I've done some work on a Tamiya Hornet RC Pi powered car; at https://github.com/lawsonkeith/picar. The original used the Pi camera which I took out as I thought it'd be too hard to control. It was only an extra 4 lines of code though in the html file.

Keith

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