AN8008 Current Measurement Error

The most annoying problem with ANENG AN8008 multimeter is the poor accuracy of high current measurements.  Significant error is seen for the measurements above 1A.  The error drifts high quickly at higher current.

It is apparent looking that the circuit board the current sense circuitry is laid out incorrectly.  The voltage measurement across the current sensing shunt includes a section of PCB trace.     The copper trace width is about 150mil, and the length is about 700mil; so the copper trace could be as much as 2-3 mOhms.  The shunt wire is labelled 0.01 Ohm.  Assume the shunt wire is Manganin with temp co 1.5e-5 /C  (vs Copper 3.9e-3 /C).  The size is about 14 AWG, so the resistance is about 2 mOhms/cm; the length appears to be 4-5cm, so 8-10 mOhms is reasonable.  We could bypass this section, but the meter may be calibrated this way. (The EEPROM may be updated for new calibration.)

The section of the PCB is already different from the earlier version based on other teardown pictures online.  The copper trace is exposed and vias are added; the trace is coated with solder.  It appears that attempts are made to improve thermal dissipation.

When I actually measured the voltage drop across the shunt wire and the copper trace, I did not see the drift that I expected.  The shunt wire has about 8 mOhms, and the trace less than 1.5 mOhms.  When 7A is applied to the meter, the area near the fuse gets pretty hot.

The burden on the current measurement is also high because of the fuse and traces.  I measured as much as 180 mOhms at the terminals.

$20 Multimeter (ANENG AN8008)

I wrote about $4 multimeter (also see here), which is fine for crude measurements.  For $20, we can have a meter with the following enhancements: 10Meg-Ohm input impedance, auto range, auto power off,  higher resolution (9999 vs 1999 counts or 4 digits vs 3.5 digits), capacitance measurement, true RMS for AC voltage and current, frequency and duty measurement, continuity beep.  Those are the features of ANENG AN8008, which has received favorable reviews online.  There are even modifications (adding capacitors to the reference and supply) to improve its performance.  The meter also comes with an extra set of probes with changeable tips.

The voltage measurements are generally very good.  The current measurements are poor at high current range.  The measurement drifts a lot.  For example, at 7A current input, the initial measurement is 7.03A (well within spec), but very quickly it drifts 7.15A and keeps climbing.  For current 1A or below, the measurements seem stable.  (It appears that the poor layout of the current sensing shunt resistor contributes to the poor performance.)  The $4 meter actual does better: measuring 7.05A and steady.  The shunt resistance in the uA range is 100 Ohms.  The resistance measurement excitation voltage appears to be 1V.  The diode voltage measurement goes up to 3V; the open circuit voltage is 3.3V .  It has a square wave output (+/-1.37V) at selected frequencies, which I don't know a good use for.  The current draw in the voltage mode is about 1.5mA from two AAA batteries; that gives about 600 hrs operating time.

The specifications are fairly conservative and easily met except for the high current measurements.

Is it worth $20?  Maybe.  It is not for professional use.  The poor high current measurement accuracy is a disappointment.  There is no 10mA and 100mA current range.  The input protection is pretty minimal: 10A/250V and 200mA/250V fuses for current protection, a bidirectional TVS diode and a 1.5K-Ohm PTC thermistor.  The 600V CAT III and 1000V CAT II ratings should not be relied on.

The Fluke 107 has comparable features and specs (the only enhanced feature is 40M-Ohm range); the cost is $80.   The extra cost buys guaranteed spec and verified 600V CAT III rating.

TS100 mini soldering iron

The TS100 soldering iron is an open source hardware by Miniware, which releases the schematics and software.  It has a decent construction; it comes with one tip but no power adapter.  The input voltage range is 12 to 24V, for power of 17W to 65W.  The interesting feature is that custom software can be loaded.  Ralim/ts100 on Github is an alternate firmware with more features.

The processor is STM32F103T8U6, 72MHz M3 core with 64K Flash and 20K SRAM, 2 12-b ADC.  It includes a 3-axis digital accelerometer for motion and orientation detection, 96x16 OLED display, a temperature sensor, TMP36 and two push buttons.  It has a barrel connector (5.5mm x 2.5mm) for power and a micro USB connector for firmware update.  The tip contains a thermocouple (reported to be type K); TMP36 provides the cold junction compensation.  The circuit design seems decent; it does not aim for the lowest cost possible.  For the price of about $50, it should not need to skimp on the circuitry.  I would estimate the bill of material costs do not exceed $20.  With 12V input, it takes about 30s to heat up to 300C; with 19V input (40W) from a laptop power adapter, it takes about 12s.

With the right firmware, it does make a nice soldering station.  The tip temperature is settable up to 450C.  The iron goes to sleep on a timer and wakes up on motion.   It can be made portable with a LiPo pack; the cutoff voltage is settable based on number of cells.  Because of the small size, a stand can be made out of a paper clip.

Habor Freight $4 Multimeter

I was generally pleased with Cen Tech multimeter from Habor Freight.  Similar looking multimeters (Item 63604) sold at Habor Freight now do not carry Cen Tech brand name; it can still be purchased for $3.99.  Upon close look the spec has changed a little bit,  The highest voltage only goes up to 250V DC or AC (vs 1000V), and the max current 5A (vs 10A).   It appears that the meter simply changed 1000V DC and 750V AC range to 250V range probably because of the fear of liability.  Opening it up, I can see the effort in cost reduction.  The Chip-on-Board I/C may be the same, but there are fewer discrete components and the PCB is smaller.   It does not have the trimmer. The fuse is soldered on; previously there was a fuse holder.  The probe is still decent; the spec says 18 gauge.  Even the critics now concede that the cheapest multimeters can be reasonably accurate; their main complaint is protections.   The CAT II rating cannot be taken serious; the CAT II marking on the probes are now removed.  One-mega-Ohm input impedance is also too much loading for some measurements.

The official spec is

• 0-200mA: 1.2%+/-2d
• 5A: 3%+/-5d
• 200mV: 0.5%+/-1d
• 2000mV-200V: 1%+/-2d
• 250V: 1%+/-2d
• AC 200/250V (45-450Hz): 1.2%+/-2d
• No accuracy given for resistance

No spec for resistance measurements.

We'll check the accuracy against a Fluke 87 (spec voltage 0.05%, current 0.2%, resistance 0.2-0.6%).  The accuracy seems to have degraded somewhat, more so with the resistance measurements.  If you accept 1% error; it is OK for casual use.

Voltage

8.8
8.8
0.00%
48.9
49.1
0.41%
98.5
98.8
0.30%
149
149.5
0.34%
198.5
198.5
0.00%
499
499
0.00%
999
999
0.00%
1999
1992
-0.35%
2.999
3
0.03%
3.999
4.01
0.28%
5
5.01
0.20%
9
9.02
0.22%
12
12.02
0.17%
15
15.02
0.13%
20
19.97
-0.15%
25
25.2
0.80%
29.99
30.2
0.70%
40
40.3
0.75%
50
50.4
0.80%

Current

17.8
17.7
-0.56%
54
54.1
0.19%
99.7
100.1
0.40%
154
154.5
0.32%
198.5
198.9
0.20%
1470
1480
0.68%
1950
1969
0.97%
5.07
5.06
-0.20%
10.21
10.19
-0.20%
15.34
15.29
-0.33%
19.6
19.52
-0.41%
50
50
0.00%
99.7
99.7
0.00%
150.8
150.9
0.07%
197.3
197.2
-0.05%
0.5
0.5
0.00%
1
0.99
-1.00%
2
1.99
-0.50%
2.999
2.99
-0.30%
3.999
3.99
-0.23%
5
4.99
-0.20%
6
6
0.00%
7
7
0.00%

* I took the current up to 7A; it is still working. I wonder if the lower spec is just to be on the conservative side.

Resistance

10.9
11.1
1.83%
50.7
50.7
0.00%
100.5
100.3
-0.20%
150.3
149.6
-0.47%
190.2
189
-0.63%
499
494
-1.00%
998
987
-1.10%
1496
1479
-1.14%
1897
1872
-1.32%
4.98
4.95
-0.60%
9.99
9.92
-0.70%
14.98
14.85
-0.87%
18.98
18.79
-1.00%
49.8
49.7
-0.20%
99.2
99.1
-0.10%
149
148.7
-0.20%
189
188
-0.53%
498
493
-1.00%
997
989
-0.80%
1494
1480
-0.94%
1895
1872
-1.21%

Performance Comparison of a few Computer Systems

Small computer modules like the Tinker Board now easily outperform old laptops while the cost ratio is 1:20.

Why is that Tinker Board runs so much faster?  Compaq Presario 2100 laptop (2003) has an Intel Celeron processor, from the Wikipedia,

Model Number	sSpec Number	Frequency	L2 Cache	FSB	Mult	Voltage	TDP	Socket	Release Date	Part Number(s)
Mobile Celeron 2.0	SL6QH (C1) SL6VJ (D1)	2000 MHz	256 KB	400 MT/s	20×	1.3 V	32 W	PPGA 478	14 January 2003	RH80532NC041256

It has 1GB RAM (max possible).  The graphic processor is ATI Radeon.  The Tinker Board has 2GB dual channel LPDDR3 RAM and a Rockchip RK3288 processor (Quad-core ARM Cortex-A17, up to 1.8 GHz and Quad-core ARM Mali-T760 MP4 GPU clocked at 600 MHz, 1MB L2 unified cache ).  The board runs on less than 5W.  Note that while everything else has improved, the processor speed has not.

The Tinker Board also compares favorably against other similar boards.  It is reported that the Tinker Board is almost twice the performance as Raspberry Pi 3.  When compiling KiCad, the Tinker Board takes about 4 hours, vs 8 hours on OrangePi Prime.  This seems consistent with some benchmarks that OPiP has a little lower performance than RPi 3.  Perhaps this justifies the twice of the cost.  Furthermore, the board quality is better.  However, while OrangePi releases the full schematics, Asus only releases the partial schematics for the Tinker Board.  Comparing RK3288 vs H5, CPU speed 1.8GHz vs 1.37GHz, about 30% faster.  So that alone does not account for the difference.  RK3288 is 32-bit architecture ARMv7-A and H5 is 64-bit ARMv8-A  (Cortex-A53 Quad-Core, 512KB L2, Mali450 MP4 GPU).  Cortex-A17 features out-of-order execution and deeper pipeline than Cortex-A53.

On Core2 Duo T7200, compiling KiCad takes about 2.5 hours with a solid state drive with 3Gb/s SATA connection.

Model number	sSpec number	Cores	Frequency	L2 cache	FSB	Mult.	Voltage	TDP	Socket	Release date	Part number(s)
Core 2 Duo T7200	SL9SF (B2)	2	2 GHz	4 MiB	667 MT/s	12×	0.95–1.175 V	34 W	Socket M	August 2006	LF80537GF0414M

All these have been single core performance. If we use all available cores, Core2 Duo still outperforms the Tinker Board, but the difference is smaller, about 30%.  Multicore improves 2.2 times for the Tinker Board and 1.6 times for Core2 Duo.  On Atomic Pi,

Model number

sSpec number

Cores

Frequency

Burst

L2 cache

GPU model

GPU frequency

Memory

TDP

SDP

Socket

Release date

Part number(s)

Atom x5-Z8350

SR2KT (D1)

4

1.44 GHz

1.92 GHz

2 MiB

HD Graphics (12 EUs)

200-500 MHz

1 × DDR3L-1600

2.17 W

2 W

UTFCBGA592

February 2016

FJ8066401836620

running 4 cores (2M L2) at 1.68GHz, the compilation takes 2.3 hours, longer than the Tinker Board, which is a little surprising.  Core2 Duo T7200 and Atom x5-Z8350 receive similar CPU Mark, but single-thread rating is much lower for x5-Z8350.The system has the advantage of having a faster disk.  A further comparison, compiling KiCad on i9-8950HK (2.9GHz/4.8GHz turbo 12MB L3) Linux Virtualbox takes only about 45 minutes.

Product Failure II

Continued from product failure.

Power Adapter

5V 2.5A AC power adapter failed.  It was still able to provide about 0.5A, but larger load caused it to turn off.  The output capacitor showed sign of heat damage.  It was a 16V 1000uF by TEAPO, but measured to have only about 5uF capacitance.  After it is replaced, the adapter worked fine with 2.5V load.  It is unclear just what caused the capacitor to overheat.

ATOTO A6 Pro

As I add to my old car more electronics, GPS, backup camera, dash cam, Bluetooth, etc, I figure all that can be handled by the Android auto head unit.  I picked up ATOTO A6 Pro for about $220.  It has the following features:

• Model Name: A6Y2721PRB (2GB/32GB);
• SoC Chip: MTK 8127A Soc-based Quad-core 1.5Ghz Cortex-A7 (512K L2) CPU with ARM Mali-450 MP4  600MHz GPU.
• Pre-Amplifier: Built-in Max 4*49W BTL Amplifier with RMS 4*29W (Vcc=14.4v,THD=10%); It can drive both 4Ω & 2Ω door speakers! 
• Preset 9-band EQ with 12 section adjustable frequency;
• Bluetooth: Dual Bluetooth (BT1 5.0 & BT2 4.0). Bluetooth1 is Qualcomm Bluetooth 5.0 w/ aptX feature, and it supports HFP/HSP/A2DP/AVRCP/PBAP;
• Radio tuner: Built-in FM/AM Radio Tuner w/ RDS (station name will be displayed if available);
• Display: Full HD 7" 1024*600 5-Touch Capacitive Touchscreen with 600cd/m² latest 178° full-viewing angle IPS display screen;
• GPS/Navigation: Builtin GPS Receiver module with external GPS antenna
• WiFi/Microphone: Builtin microphone & Ultra external Wi-Fi antenna (Silver plated copper wire) and external microphone
• Input/output
• Reversing camera input
• Front camera input
• AUX Audio/Video input
• 4-CH RCA Audio Out (4V) for connecting to amplifiers
• Separate Sub-woof Out (4V) (Manual /Automatic mode available)
• Steering wheel control input
• One Micro SD slot
• 3 USB interfaces, one of which is a quick charge (2A) port

The harness has the following connections

This model has physical buttons, no gesture control.  Having physical buttons is useful because the it is harder to operate the touchscreen while driving.  But in any case, a rotary switch would be better for such things as changing volume. 

When ignition is off, it draws about 18mA.  The standard battery is 45Ahr.  So it is about 1% a day.   It takes 2 seconds to be on after the ignition is on.  When idle, it draws about 700mA.  When in standby, it draws about 330mA.

Installation is not too difficult after watching a number of online videos.