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I have two? One with a grid (really, a 6c4) and the other a fet.
Handy thing they are.?
I've even copied W1AW with one!
Allison
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DuWYne kv4qb
Very impresive.? That fits with what this group was envisioned being....Amateur designed and built test equipment that is equal to or better than available lab-grade equivalent commercial gear.?? ? Very good job.
Arv? k7hkl _-_
Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message -------- From: DuWayne Schmidlkofer <duwayne@...> Date: 9/23/18 8:29 AM (GMT-08:00) Subject: Re: [HBTE] #Differential_Voltmeter
I use the Adafruit ADS1x15 library?? .? It works for either the 12 or 16 bit version of the chip. There are examples for the differential or single ended use.? I just use one of the inexpensive modules I got off of eBay for less than $4. Here is a test gadget I built using it in single ended mode, with all four inputs used. ? DuWayne,? KV4QB
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I use the Adafruit ADS1x15 library?? .? It works for either the 12 or 16 bit version of the chip.
There are examples for the differential or single ended use.? I just use one of the inexpensive modules I got off of eBay for less than $4.
Here is a test gadget I built using it in single ended mode, with all four inputs used.
?
DuWayne,? KV4QB
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Jim
Looks like I missed that in the posted version.? Thanks for catching it.
I am away from home today but will make correction when i get back.??
Arv _-_
Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message -------- From: Jim Purvis <jimpurvis7474@...> Date: 9/21/18 8:08 AM (GMT-08:00) Subject: Re: [HBTE] #Differential_Voltmeter
Thanks. I guess the best way will be to build and test. More fun that way anyway.? Also just a note for you and those that might build this. ?Found a small error in the code. ? In reading ADC a. See snippet.? a = analogRead(0);? a = analogRead(1);? // read ADC-0 twice to normalize sampling capacitor? A = a * (5 / 1023.0);?? // converts ADC-0 out to volts??????????????? delay(3000);? b = analogRead(1);? b = analogRead(1);? // read ADC-1 twice to normalize sampling capacitor
Thanks jim
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With a few minor code changes I have this meter running. Have not completed testing yet but your right. Sensitivity and resolution could be better.?
DuWayne... could you share your code?
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For differential voltage measurements I have been using an add on ADS1115 I2C 16bit ADC module.? Can be programmed for either 4 single ended or 2 differential inputs.? Higher resolution and? input resistance than just the Arduino alone.??With just the Arduino I usually had to add a buffer op-amp to get the input resistance up to what I needed.? It also has a programmable gain amplifier that makes it very sensitive,? I have used it to measure voltage drop across long circuit board traces.?
--
DuWayne,? KV4QB
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Thanks. I guess the best way will be to build and test. More fun that way anyway.?
Also just a note for you and those that might build this. ?Found a small error in the code. ? In reading ADC a. See snippet.?
a = analogRead(0);
? a = analogRead(1);? // read ADC-0 twice to normalize sampling capacitor
? A = a * (5 / 1023.0);?? // converts ADC-0 out to volts
??????????????? delay(3000);
? b = analogRead(1);
? b = analogRead(1);? // read ADC-1 twice to normalize sampling capacitor
Thanks
jim
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Jim? WA7HRG
Two ways to determine the input resistance of any measuring device. - ?Add series resistance to the input until measured voltage reads half what it
did without the resistance.? This external resistance is then the same as the
internal input resistance.
- ?Add a large series resistor (100K or greater) and measure voltage drop across
this resistor while measuring a voltage near the maximum input.? Then calculate
current through this added resistor and use that to derive input resistance for the
meter from current and voltage at the meter input.
This gets tricky with some ADC devices because the charge capacitor in sample-and-hold
circuits causes different current flows based on left over charge from a previous hold action. This is partially why in my code I read the ADC input twice and take the second reading as
being the most accurate.?
Arv? K7HKL _._
Arv
interesting project. Do you know or can you tell me how to find out the input resistance of such a meter?? I don’t seem to find it on the Arduino spec sheet.?
When building an RF probe the series resistor is calculated based in meter input resistance.? Yes, not critical if all you need are relative readings or differential gain/loss measurements.? But would be nice to have the reading somewhat accurate.?
Jim
wa7hrg
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Arv
interesting project. Do you know or can you tell me how to find out the input resistance of such a meter? ?I don’t seem to find it on the Arduino spec sheet.?
When building an RF probe the series resistor is calculated based in meter input resistance. ?Yes, not critical if all you need are relative readings or differential gain/loss measurements. ?But would be nice to have the reading somewhat accurate.?
Jim
wa7hrg
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Allison
Agreed about noise from all sort of electronics.? We live in a world full of it, some of our
own making.?
I broke open the USB charger module (1) to see what was in it, and (2) so others would
not have to do the same.? Now that I know what is inside and how it works I can simply
purchase those little 5V chargers and use them much like we have done with wall-warts
for many years.? A USB cable from the dollar store and small test equipment is easily
and conveniently powered.?
These USB chargers seem to operate at around 50 KHz (the pulse rate varies depending
on current load), but do not radiate strongly.? Opening one up and adding 0.1 mfd across the
5V output quieted it down to almost nothing being radiated.?
The 5V output is unexpectedly stable with varying load, at least on these units from a local
Dollar Store.? Since Li-ion cells act like big capacitors I tried using one of these 5V chargers
to power a Pixie based telemetry system that has Li-ion backup power.? Result is gratifying,
no switching transients, and It works just like it does when running on Li-ions charged by a
pair of small solar cells.? The telemetry system runs on Pixies at 160 to 190 KHz but no
noticeable interference from the 5V charger.?
Of course the 5V output is excellent for Arduino Nano? or Arduino Pro-mini based test
equipment.?
Arv _._
On Wed, Sep 19, 2018 at 8:28 PM ajparent1/kb1gmx < kb1gmx@...> wrote: Arv,
as an actve ham on MW, HF and VHF? II can say those things and may other not USB are
Banned in teh hose till verified RF non interfering.? Can't control the neighbors but I try
to not do it to myself.?
For bench use USB power I have a box with six 7805 analog regulators, some with
USB connectors, some power-pole, and binding posts.? Each does an amp easy.
and the transformer, rectifier and filter (times two) feeds each of three so?I can
have two floating sources without common ground.
Electrical noise at the bench can be an annoying.
Allison
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Hey Arv,
Handy, you bet!
Been using those for something north of 40 years.? Back then it was to make
digital computers using Z80 and friends without resorting to back planes
(large or costly) to route bussed signals to stacked cards.? Worked well
and cheap too.? I still have a bin of those 60 wide ones that are easily
cut and handy for Arduino work.
Allison
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Arv,
as an actve ham on MW, HF and VHF? II can say those things and may other not USB are
Banned in teh hose till verified RF non interfering.? Can't control the neighbors but I try
to not do it to myself.?
For bench use USB power I have a box with six 7805 analog regulators, some with
USB connectors, some power-pole, and binding posts.? Each does an amp easy.
and the transformer, rectifier and filter (times two) feeds each of three so?I can
have two floating sources without common ground.
Electrical noise at the bench can be an annoying.
Allison
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Building small test equipment modules usually involves some sort of power system.? Batteries
are a good start but for equipment that is only used on the workbench it seems that an AC supply
is a better idea.? Problem is that many of our newer design homebrew test equipment does not
require high voltages or high current, and does not need physically large mains based power
supplies.? This situation prompted me to take a deeper look at AC-to-USB phone chargers and
how they might be adapted for use in homebrew test equipment.?
This AC mains to USB charger for cell phones was purchased at the local Dollar Store
for US$1.07,? including sales tax.? One end has plug-in prongs for a mains outlet.?
The opposite end has a standard USB jack for the cell phone charging cord.
Specification printed on the case indicate output is 5.0V at up to 1A.? That should
be adequate for small homebrew test equipment needs.??? When I plugged this charger
into AC mains and measured the 5V output with no load it was exactly 5.00 volts.
After hammering around the end to break the glue loose I found that the AC prongs are
only spring-contacted to actual PCB input.? Assumption is that this arrangement allows
other country style plug prongs to be installed.?
Top view of the charger PCB.? USB jack is on the left and AC input is on the right.
PCB bottom view shows full-wave rectifier at top-left corner.? A CP5212 control IC is
below and to the right of that.? Another rectifier is in the lower right corner.?
I could not find a schematic for this particular unit but most of what I did find on-line
looks approximately like the design shown above.? This appears to be a switching circuit
with feedback control from the right side of the circuit.? Typical specification on various
sites indicate that isolation between AC input side and DC output side is in the area
of 2000 volts.?
Next effort will be to measure and document the amount of AC and DC leakage between
AC side and DC side.? Then I can start working on using one of these tiny power supplies
inside a piece of homebrew test equipment.
This picture shows a work-in-progress AD9850 DDS VFO / Signal Generator, with
the AC-to-USB power unit sitting bottom-center in the clear plastic chassis.? This
power unit will have to supply 5V for the LCD & backlight, Arduino Pro-Mini, and
the DDS board.?
More info will be provided as work progresses.?
Arv _._
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Cool Stuff Arv. I was thinking more about PCBs and perhaps a concept that can become more functional, than the Arduino boards with their funky connectivity being limited to a single mezzanine add on board. I played around with shifting pin locations in order to get additional layers; however, this is not a logical direction to go. As I already mentioned, I had a very good experience in the past with Multi-layer Double DIN stacked boards with feed through DIN connectors and Banana plug/jack combination for high current distribution between layers.
I like you creativity.
--Ron? ? N7FTZ
Ron N7FTZ
A stack of those cheapest of cheap prototype boards is a perfect fit for standard size mains
outlet boxes, the kind that sell at US DIY Hardware stores (Lowes, or Home Depot) for
US$0.49 each in singles and for $0.39 each if you buy then by the dozen.
Four boards in a stack fit into the box and allow enough space for front-panel switches
and potentiometers, and even an LCD display.
That pretty well solves the chassis problem for small systems.? For larger systems
these outlet boxes can be sawed apart and glued up into larger boxes using solvent
glue intended for PVC lawn sprinkler pipe.? Clamp the glued boxes overnight and
the joints will be as strong as the original box.?
My own interest is in building test equipment.? Avoiding wasted time trying to figure
out some sort of protective chassis is always a priority.? This is what comes out of
that situation.??? 8-)
Arv? K7HKL _._
This type of interconnect makes a lot of sense. I used it many times in the past with industrial products and the products were very stable both mechanically and electrically. Modular design has many advantages for products that offer multiple hardware options. Perhaps we can start by figuring out the board dimensions and match to potential standard metal or plastic cases.
--Ron? ?N7FTZ
Bi-sexual connector blocks, inexpensive from Ebay vendors.
Connectors on each end of cheap prototyping boards from Ebay vendors.
I took the suggestion of John VK6JY and used connectors on each end of the
proto-boards.? This means the boards can be stacked or plugged together in an
offset layout.?
A block of 5 prototype boards with connectors soldered in place and the boards plugged
together.
Alternative configuration to allow taller components on some boards.
Actually I am rather happy with the way this worked out.? Next question is "what to build
on my modular cube?".? I ohmed out all the pins and have connectivity where it should
be and no shorts where they should not be any.? Doing this again I might cut the pins a
bit shorter because the socket sides do not press all the way down to the board surface.
The slightly more expensive boards with plated-through holes should be even better.? I
have some of those on order from Ebay vendors.
The idea is to build circuits in modular form so that sections can be rebuilt or replaced
without disturbing the whole circuit.? Power and control signals will be via the connectors
and signals (RF, IF, AF, etc) will be connected by small coaxial plug lines along the edges
of each board.
Arv? K7HKL
_._
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Ron N7FTZ
A stack of those cheapest of cheap prototype boards is a perfect fit for standard size mains
outlet boxes, the kind that sell at US DIY Hardware stores (Lowes, or Home Depot) for
US$0.49 each in singles and for $0.39 each if you buy then by the dozen.
Four boards in a stack fit into the box and allow enough space for front-panel switches
and potentiometers, and even an LCD display.
That pretty well solves the chassis problem for small systems.? For larger systems
these outlet boxes can be sawed apart and glued up into larger boxes using solvent
glue intended for PVC lawn sprinkler pipe.? Clamp the glued boxes overnight and
the joints will be as strong as the original box.?
My own interest is in building test equipment.? Avoiding wasted time trying to figure
out some sort of protective chassis is always a priority.? This is what comes out of
that situation.??? 8-)
Arv? K7HKL _._
This type of interconnect makes a lot of sense. I used it many times in the past with industrial products and the products were very stable both mechanically and electrically. Modular design has many advantages for products that offer multiple hardware options. Perhaps we can start by figuring out the board dimensions and match to potential standard metal or plastic cases.
--Ron? ?N7FTZ
Bi-sexual connector blocks, inexpensive from Ebay vendors.
Connectors on each end of cheap prototyping boards from Ebay vendors.
I took the suggestion of John VK6JY and used connectors on each end of the
proto-boards.? This means the boards can be stacked or plugged together in an
offset layout.?
A block of 5 prototype boards with connectors soldered in place and the boards plugged
together.
Alternative configuration to allow taller components on some boards.
Actually I am rather happy with the way this worked out.? Next question is "what to build
on my modular cube?".? I ohmed out all the pins and have connectivity where it should
be and no shorts where they should not be any.? Doing this again I might cut the pins a
bit shorter because the socket sides do not press all the way down to the board surface.
The slightly more expensive boards with plated-through holes should be even better.? I
have some of those on order from Ebay vendors.
The idea is to build circuits in modular form so that sections can be rebuilt or replaced
without disturbing the whole circuit.? Power and control signals will be via the connectors
and signals (RF, IF, AF, etc) will be connected by small coaxial plug lines along the edges
of each board.
Arv? K7HKL
_._
|
This type of interconnect makes a lot of sense. I used it many times in the past with industrial products and the products were very stable both mechanically and electrically. Modular design has many advantages for products that offer multiple hardware options. Perhaps we can start by figuring out the board dimensions and match to potential standard metal or plastic cases.
--Ron? ?N7FTZ
Bi-sexual connector blocks, inexpensive from Ebay vendors.
Connectors on each end of cheap prototyping boards from Ebay vendors.
I took the suggestion of John VK6JY and used connectors on each end of the
proto-boards.? This means the boards can be stacked or plugged together in an
offset layout.?
A block of 5 prototype boards with connectors soldered in place and the boards plugged
together.
Alternative configuration to allow taller components on some boards.
Actually I am rather happy with the way this worked out.? Next question is "what to build
on my modular cube?".? I ohmed out all the pins and have connectivity where it should
be and no shorts where they should not be any.? Doing this again I might cut the pins a
bit shorter because the socket sides do not press all the way down to the board surface.
The slightly more expensive boards with plated-through holes should be even better.? I
have some of those on order from Ebay vendors.
The idea is to build circuits in modular form so that sections can be rebuilt or replaced
without disturbing the whole circuit.? Power and control signals will be via the connectors
and signals (RF, IF, AF, etc) will be connected by small coaxial plug lines along the edges
of each board.
Arv? K7HKL
_._
|
Bi-sexual connector blocks, inexpensive from Ebay vendors.
Connectors on each end of cheap prototyping boards from Ebay vendors.
I took the suggestion of John VK6JY and used connectors on each end of the
proto-boards.? This means the boards can be stacked or plugged together in an
offset layout.?
A block of 5 prototype boards with connectors soldered in place and the boards plugged
together.
Alternative configuration to allow taller components on some boards.
Actually I am rather happy with the way this worked out.? Next question is "what to build
on my modular cube?".? I ohmed out all the pins and have connectivity where it should
be and no shorts where they should not be any.? Doing this again I might cut the pins a
bit shorter because the socket sides do not press all the way down to the board surface.
The slightly more expensive boards with plated-through holes should be even better.? I
have some of those on order from Ebay vendors.
The idea is to build circuits in modular form so that sections can be rebuilt or replaced
without disturbing the whole circuit.? Power and control signals will be via the connectors
and signals (RF, IF, AF, etc) will be connected by small coaxial plug lines along the edges
of each board.
Arv? K7HKL
_._
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contact me at? fernandocasari@...? My english is very limited to follow a tread here best to all? Fernando
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DuWayne Schmidlkofer