The below device cost a few dollars and I picked up a 3 1/2 digit DPM with 0.56 inch high digits off of ebay for about $8.00 including shipping. The DPM will be mounted up on the wall so it will be easy to see what the DCC current is like at any time.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Below is the LED DPM meter that will be mounted on the wall. Right now we have a small LCD DPM on the dispatchers panel but the LED DPM will be easier to read.
The DPM requites 5 volts DC so I cobbled together some parts from my junk box. Two caps and a low power, 250ma, 5 volt regulator. We have a 12 volt DC buss for operating slow motion machines so it is easy to pick off 12 volts DC and add a regulator.
IMPORTANT, if you use this circuit with a DPM, make sure the DPM has isolated ground or you might let out some smoke. Some DPM meters have isolated ground, some do not. If all else fails, try to read the instruction sheet first.
For short term, many inexpensive digital multimeter work just fine. I did that until I purchased the DPM.
Is there a good way to calibrate this meter system?
73
Bruce in the Peg
My version is a couple years old. I used a DC supply for calibration. I used a digital 'Scope to verify.
Below is the upgraded version.
http://home.cogeco.ca/~rpaisley4/DCCammeter10.html
He does answer email.
Blind BruceIs there a good way to calibrate this meter system?
I used a DC power supply into a low resistance high wattage resistor and set the supply for 2 amps. I then tweaked the DPM for 2.00. The red LED DPM with 0.56 inch high digits is set about 7 feet above the layout where everyone can see it quite well.
The current monitor circuit uses two 0.1 ohm, 1 percent resistors.
We use the NCE Power Pro 5 amp system. If we get a short, the meters show 4.9 amps, then zero amps as the system cuts out. Close enough for us.
With ten sound locos running this past Monday, we could see around 3 amps.
Here is a photo of the LED DPM with 0.56 inch high digits which is about 8 feet above the floor and visible to the layout room.
Below is the LCD DPM with 0.5 inch high digits which is in the dispatcher's panel and not easily visible to the users.
One more item, the two DPM power packs are plugged into a surge protector device that controls all the mains power for the layout. I mention that because some people have problems with a wall wart that has no power switch.