Products > Test Equipment
AN8008 US $19, 9999count, 1uV, 0.01uA, 0.01Ohm, 1pF resolution meter
Gandalf_Sr:
--- Quote from: ocw on July 24, 2017, 12:33:16 am ---
--- Quote ---1. Change Amps to mA - I know you've stated that it can be done by changing shunt resistors but can the EEPROM also be hacked to give the correct display? I don't want to measure Amps, just mA and uA.
--- End quote ---
I changed the 0.01 ohm shunt resistor for the AmA jack to 0.095 ohms and now with the leads in the COM and AmA jacks, but the AN8008 rotary switch in the uA position, I measure mA current up to 99.99 mA with 0.01 mA resolution and 0.1 mA resolution up to 999.9 mA with the decimal in the correct location. 999.9 mA is the maximum current which can be read now. The mA readings are now typically 0.35% high. I haven't tried to change the meter's software yet. Others might need a slightly different value shunt resistor.
--- End quote ---
Thanks, what size is that 0.095 Ohm resistor? (my AN8008 hasn't arrived yet).
ocw:
--- Quote ---Thanks, what size is that 0.095 Ohm resistor?
--- End quote ---
While a resistive wire resistor like a 0.1 ohm IRC OAR1R100FLF would be best due to its 20 PPM/C temperature coefficient, they are not available in odd values. Because of that I went with two 0.0475 ohm Vishay RCWH080547L5FNEA 200 PPM/C 1/3W resistors in series. With the one amp current maximum with that modification they would each dissipate 0.0475 watts and would have a collective burden voltage of 0.095 volts. You need remove some solder mask to conveniently install the new resistors.
You would probably end up with a lower temperature coefficient using the mentioned 0.1 ohm resistor with a 2 ohm resistor in parallel with it. This might make it easier to fine tune the resistance to "calibrate" it. A 10% value change in the 2 ohm resistor value will only change the parallel resistance by 0.43%. I might try that.
floobydust:
Missing are the 9.999mA and 99.99mA ranges.
Right now, it has 10mR and 100R shunts only. The hardware (range switch) needs to switch in R24 1R shunt (J4/R14 in the generic schematic) to the input jack. If you look at the PCB you will see nothing connected to R23/R24 junction.
Then you need the MCU firmware to enable this function, and it has separate CAL factors for the ranges. The MCU firmware probably supports this- the predecessor 6,000 count DMM IC has those ranges under function code 0EH, 0DH which is not used in my AN8008 EEPROM dump. The predecessor IC has no 60.00uA (99.99uA) range but the new IC does.
I haven't had time to try it.
Notice the meter has Hz/%duty cycle twice on the rotary switch. I think they screwed up on the design a bit.
floobydust:
--- Quote from: plazma on July 23, 2017, 12:16:20 pm ---
--- Quote from: floobydust on July 22, 2017, 08:14:49 pm ---RS-232 output - I can't see the IC TXD pin bonded.
--- End quote ---
How did you check this?
For one AN8002 unit I removed die potting epoxy to reveal pin 20 pcb pad. I added a pull-up resistor and measured the signal. Nothing was visible. I sacrificed this unit and removed the potting epoxy to reveal the bonding wires and the die. The pin was unbonded.
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For lowest cost, I assumed unused pins would not be bonded out. TXD would be very useful for testing.
Here is the region on the PCB I guessed TXD would be brought out. I do not see any traces there, however I do not have the exact die pinout. I'm not using the QFP pinout.
What are you using for a solvent on the encapsulant? TXD may very well be accessible.
plazma:
--- Quote from: floobydust on July 24, 2017, 06:20:09 pm ---
--- Quote from: plazma on July 23, 2017, 12:16:20 pm ---
--- Quote from: floobydust on July 22, 2017, 08:14:49 pm ---RS-232 output - I can't see the IC TXD pin bonded.
--- End quote ---
How did you check this?
For one AN8002 unit I removed die potting epoxy to reveal pin 20 pcb pad. I added a pull-up resistor and measured the signal. Nothing was visible. I sacrificed this unit and removed the potting epoxy to reveal the bonding wires and the die. The pin was unbonded.
--- End quote ---
For lowest cost, I assumed unused pins would not be bonded out. TXD would be very useful for testing.
Here is the region on the PCB I guessed TXD would be brought out. I do not see any traces there, however I do not have the exact die pinout. I'm not using the QFP pinout.
What are you using for a solvent on the encapsulant? TXD may very well be accessible.
--- End quote ---
There is a IC (QFP) footprint under the encapsulant. The die is bonded to the inner end of the pads. So you can carefully remove the encapsulant to reveal the outer end of the pads without harming the bonding wires. I just used hot air to soften the encapsulant and removed it carefully with a surgical knife. The TX pad is the fourth from the top on the left side in your image. Check the DTM0660 datasheet pinout.
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