Regarding the ICL 7107 based panel meters is there a particular spec or version I am looking for? Like 0-15v 0-3a or is that not a factor? The expense is less of a concern to me than quality. I don't expect this project to be a bargain.
...
As mentioned before in this thread (by pqass I think), the HP has a very large aluminum heatsink that is basically the whole back panel of the device. The Darlingtons were mounted on a small porches on each end of the heat-sink. I know there will be a lot of heat to reject. I plan on mounting the Darlingtons on small aluminum heat-sinks maybe even fan cooled if that's even possible (I don't know). At minimum I planned on a cased mounted fan to circulated air through the cabinet. Maybe even get fancy a use a thermistor circuit to control a fan. I would have to research that a bit. I don't want to have a heat issue. Is this over kill?
I'm searching Google Shopping or Amazon for "digital panel meter". There are so many that aren't useful to your application. Like:
- 2 wire only; only good for 2.5VDC to 100VDC
- AC input
- ammeters with built-in shunt or AC current transformer (torroid)
- combination voltmeter and ammeter
- frequency meter, tachometer, counter
For those that have a power pair (5VDC) AND a sense wire (single or pair), no information is provided on how to configure it or about power isolation with regards to the sense inputs. Ideally, you need a meter with a separate power pair AND 0-200mV (full-scale) sense inputs (with IN-LO/-Vsense that can be tied to supply ground). Most people won't know how to configure the resistor divider for their application, hence, you'll see 5, 20, 50, 100, 200, 500V in the description.
You can find exactly what you need for name brand meters like the
Murata DMS-20PC series but then you're looking at >$60!
As I'd said earlier, an ammeter is just a voltmeter that measures across a shunt so you can buy the same panel meter to do both power supply output voltage monitoring and ammeter service. We don't want to add another shunt (for reasons see my reply#36) as we already have R2.
However, hope may not be lost if we take a bit of a gamble.
If you search for "digital panel meter 5135" you'll see the attached. They are sold by many suppliers
like this one. According to the
ICL7107 datasheet, Figures 13, 14, IN-LO/-Vsense can be connected to GND if it has an external reference (TL431 seen in another photo) and -5V supply is provided, both of which may be true in the photo.
To use this meter, you'd just need a 7805 similarly configured like the 7812 from the same transformer's unregulated positive in the op-amp supply; no need for another isolated 5V display supply. DO NOT USE the +5VREF label to power the panel meters.
For the ammeter configuration up to 1.999A, R12=0R (a short), R11=open/no populate. For one up to 19.99A, R12=10K, R11=100K. Short the "2" or "20" option on the panel meter to enable the correct decimal point (0-1.999A vs 0-19.99A). IN-HI of the meter is on the common of SW1A switch, IN-LO on [+S]/GND/+OUTPUT post. HOWEVER, R20 wiper is a negative voltage! To turn it positive, you'll need an inverting opamp. See attached panel meter wiring schematic.
The voltage monitor panel meter can also use the same op-amp power supply's new 7805 positive output and GND. With IN-LO tied to [+S]/GND/+OUTPUT post and IN-HI tied to the R18=10K/R17=900K divider. HOWEVER, it too will report a negative voltage, thus, another inverting opamp will be needed. See attached panel meter wiring schematic. Short the "20" option on the panel meter for 0-19.99V.
WRT heatsinks...
CPU heatsink+fans can transfer lots of heat in a compact space.
Attach on back of enclosure or at least exhausting the fan out the back.