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by BudBennett
Sat Oct 31, 2015 6:11 am
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Hi Jarrah31,

Yes, the device you spec'd is good for Q1. The -80V CBO breakdown is because it is a PNP transistor instead of an NPN. Let me know how it turns out.

Bud.
by BudBennett
Wed Oct 21, 2015 3:32 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

I picked the BC856B because the min beta (current gain) is 220 and the CBO breakdown is 80V (and it's cheap - $0.04 at TaydaElectronics.com ). Yes LVCBO is the same as BVCBO - it is the voltage that the device is able to withstand across the collector-base with the emitter open circuit. The CEO brea...
by BudBennett
Wed Oct 21, 2015 1:55 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Jarrah31, Both of your BC856B options are rated 80V for LVCBO (check the data sheet), so you can go either way. The working voltages of the 1/4W resistors you found is 1600V, so they should work as well. The tantalum capacitors you found vary in price according to tolerance and series resistance. In...
by BudBennett
Tue Oct 20, 2015 11:48 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Jarrah31, The Stackpole resistors have a working voltage of 1150vrms. Try searching for "resistor working voltage 1000V" or such to see what comes up. If you aren't going to use my custom PCB then you can probably get away with using 2 resistors in series instead of the Stackpole resistors. As far a...
by BudBennett
Fri Sep 18, 2015 3:04 pm
Forum: Automation, sensing and robotics
Topic: Raspi-powered seismometer/seismograph
Replies: 63
Views: 38786

Re: Raspi-powered seismometer/seismograph

Also I think that I can reduce the number of magnets by a factor of 2 by locating the damping plate further out on the beam. I believe that the original design needed to keep the damping magnet some distance from the sensing coil to avoid interaction. Since this design is not sensitive to magnetic f...
by BudBennett
Fri Sep 18, 2015 2:59 pm
Forum: Automation, sensing and robotics
Topic: Raspi-powered seismometer/seismograph
Replies: 63
Views: 38786

Re: Raspi-powered seismometer/seismograph

I can't claim the ball point hinge as mine. Dr. Peters suggested it a while ago and I thought that I'd try it. Here's a detail of the hinge: ballpointHinge-s.jpg I used two "free" pens from the local bank. Ripped the ink tubes of of the tips and epoxied them into a modified U-channel piece. The two ...
by BudBennett
Thu Sep 17, 2015 11:12 pm
Forum: Automation, sensing and robotics
Topic: Raspi-powered seismometer/seismograph
Replies: 63
Views: 38786

Re: Raspi-powered seismometer/seismograph

Here are a few photos of the seismometer, hinge and sensor. I think you can tell how it is put together from these. WorkingPrototype-s.jpg Hinge-s.jpg SideViewOfSensor-s.jpg I built two hinge types: the hinge shown uses blister pack plastic as the flex material. I had tried strips of aluminum (alumi...
by BudBennett
Thu Sep 17, 2015 6:59 pm
Forum: Automation, sensing and robotics
Topic: Raspi-powered seismometer/seismograph
Replies: 63
Views: 38786

Re: Raspi-powered seismometer/seismograph

I have finally gotten to the point where I can talk about my home-built seismometer. I figure it’s either put up or shut up, so I have some plots of real quakes in this post. It is constructed pretty much as per my previous posting. I replaced the box cutter blade hinge with a hinge that would bette...
by BudBennett
Sun Jun 28, 2015 3:35 pm
Forum: Automation, sensing and robotics
Topic: ADC for bipolar signal
Replies: 2
Views: 817

Re: ADC for bipolar signal

The simplest way (with its own set of problems) is to use two resistors to level shift the signal up into the range of your ADC. Here's a schematic: Circuit.png The resistors should be the same value and of a value that won't load your signal source or present problems to your ADC, both of which are...
by BudBennett
Sun Jun 07, 2015 5:15 pm
Forum: Automation, sensing and robotics
Topic: Raspi-powered seismometer/seismograph
Replies: 63
Views: 38786

Re: Raspi-powered seismometer/seismograph

I'm ready to begin a seismometer project. I'm trying to keep the cost as low as possible while still yielding a reasonable instrument. My expertise in in electronics but the mechanical stuff is more problematic. So far I have only roughed out a hardware approach -- I'm hoping to use some ready-made ...
by BudBennett
Wed May 06, 2015 3:42 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Yes, I cover the CT interface in my rather longish post above. The half-wave rectifier will work, but I'm a bit paranoid about the stuff that you don't plan for - like a large transient spike that blows up the Pi. I'd rather replace a circuit that costs $0.25 than the entire PI, which is doing many ...
by BudBennett
Wed May 06, 2015 1:25 am
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Reading down a bit further you'll find the following:

"Design for Reliability guidelines suggest that resistors be derated to 60% of maximum operating limits for voltage and power dissipation."

A working voltage of 250V doesn't cut it.

Bud.
by BudBennett
Mon May 04, 2015 8:56 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 16774

Re: Detecting 250VAC voltage/current of deep well pump motor

Reagen, The GPIO must be configured with an internal pullup or it will always have a low voltage when read by a voltmeter. You must set the GPIO to be a pullup with the following python code: # set up GPIO pullups and interrupt on GPIO24 GPIO.setmode(GPIO.BCM) GPIO.setup(25, GPIO.IN, pull_up_down = ...
by BudBennett
Sun Jan 25, 2015 4:55 pm
Forum: Automation, sensing and robotics
Topic: Circuit design help (home heating)
Replies: 10
Views: 2270

Re: Circuit design help (home heating)

As you said, there are many ways to accomplish this. Here's a block diagram (not in crappy ASCII) of what I think you wish to accomplish: HeatingSystem.png Since the thermostat wires are already in place I would suggest that you use them and hardwire the temperature sensors to the controller (the Pi...
by BudBennett
Sun Jan 25, 2015 5:53 am
Forum: Automation, sensing and robotics
Topic: Circuit design help (home heating)
Replies: 10
Views: 2270

Re: Circuit design help (home heating)

It sounds like you want to replace the current thermostats with the z-wave thermostats and use the domoticz for logging and user interface. I think that you are asking about the best method for interfacing to the PLC and possibly the zone control valves. I have a 9-zone in-floor heating system that ...
by BudBennett
Sat Jan 24, 2015 6:09 pm
Forum: HATs and other add-ons
Topic: What's the use of U14 (dual PNP transistors) around P-FET?
Replies: 4
Views: 2677

Re: What's the use of U14 (dual PNP transistors) around P-FE

It is a closed loop unity-gain AMPLIFIER, with an offset. I am uncertain about the true schematic values because the Adafruit schematic shows both resistors as 10k, but the GitHub schematic has the bias resistor, R2, as 10K, and the load resistor, R3, as 47k. I believe that the GitHub values are mor...
by BudBennett
Tue Dec 16, 2014 8:05 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: i2c driver data race
Replies: 9
Views: 1856

Re: i2c driver data race

Thanks for posting about this. I have 3 i2c devices under the control of a single process. I wanted to add a 1307 RTC, which is under the control of a system process. I got a small non-catastrophic-failure rate (only on the RTC query) when testing for bus collisions so haven't attached the RTC. Want...
by BudBennett
Sun Dec 14, 2014 4:30 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi Thermostat
Replies: 19
Views: 4294

Re: Raspberry Pi Thermostat

Most people are trying to replace the thermostat with the Raspberry Pi. There would be no need to interface with the thermostat. The Pi would need to interface with the heating system "controller". Here in the U.S. the most common heating system interface uses 24VAC, so you would require the Pi GPIO...
by BudBennett
Tue Nov 25, 2014 9:49 pm
Forum: Automation, sensing and robotics
Topic: "Real" temperature / humidity sensor?
Replies: 5
Views: 1957

Re: "Real" temperature / humidity sensor?

Well...as I said, I was not too concerned about absolute accuracy. So I found a digital thermometer that I "trusted" to within 0.25C or so. I grouped this thermometer with all of the thermistors that I wanted to calibrate. Then I forced air from a fan blown over the group of sensors. I found that if...
by BudBennett
Tue Nov 25, 2014 8:15 pm
Forum: Automation, sensing and robotics
Topic: "Real" temperature / humidity sensor?
Replies: 5
Views: 1957

Re: "Real" temperature / humidity sensor?

I can only speak for temperature sensors. A simple thermistor can yield accuracies around 0.02 degrees C for a range of less than 100C. You must use a linearization equation (Steinhart-Hart) which some thermistor manufacturers provide coefficients for. You must also correct for offset errors by plac...
by BudBennett
Sat Oct 04, 2014 3:10 pm
Forum: Automation, sensing and robotics
Topic: Battery Cell Voltage Sensor
Replies: 13
Views: 5777

Re: Battery Cell Voltage Sensor

PiGraham, The LTC6801 is a basic monitor, but the LTC6802 allows the 12-bit ADC result to be accessed by the SPI interface. The ADC doesn’t care if the cell is Li-ion or lead-acid - the ADC has a cell range of 0-5V. Here is a link to an application example: http://sourcelion.wordpress.com/2014/07/20...
by BudBennett
Fri Oct 03, 2014 10:59 pm
Forum: Automation, sensing and robotics
Topic: Battery Cell Voltage Sensor
Replies: 13
Views: 5777

Re: Battery Cell Voltage Sensor

I assume that your cells will be stacked serially (you did not specify). Have you looked at the LTC6801-LTC6804 multi cell battery stack monitors? They are setup for automotive applications. Each LTC680X can monitor 12 cells, but can be daisy chained to monitor up to 1000V. It looks like a neat solu...
by BudBennett
Wed Jul 23, 2014 5:03 am
Forum: Automation, sensing and robotics
Topic: 24-bit 16Channel ADC with 16 digital I/O expansion PCB
Replies: 24
Views: 15444

Re: 24-bit 16Channel ADC with 16 digital I/O expansion PCB

etrash, My board only has 14 single-ended channels, so you will need more than 8 boards for 120 system channels. Also, each board will have it's own reference so you will have to manage that unless you depopulate the 3.3V regulator on all but one board and feed the 3.3V supply to all of the other bo...
by BudBennett
Tue Jul 22, 2014 1:09 am
Forum: Automation, sensing and robotics
Topic: 24-bit 16Channel ADC with 16 digital I/O expansion PCB
Replies: 24
Views: 15444

Re: 24-bit 16Channel ADC with 16 digital I/O expansion PCB

This is the link to a dropbox directory containing the gerber files that were used to create the PCB with OSH Park: https://www.dropbox.com/sh/3xz7ovh7jcfghr0/AADEP-lw-yAWMYAi4lGD86FFa/TempController You will find a BOM in that directory as well. Let me know if the BOM has sufficient info. This is t...

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