21 July 2022

SGS integrated circuits H100/H200 series

Shortly after posting about H 257 and H 258 never-seen-before(-by-me) ICs, I tried different search keywords and a datasheet popped up from the back of Internet.

According to that document SGS-ATES produced a series of High Level Logic I.C.'s designed specifically for applications in areas where noise is a hazard. The supply voltage is from 10.8 to 20V and they are compatible with MOS technology:


From the datasheet you learn that the suffix D1/D2/D6/B1 distinguishes between voltage+temperature range and case material. I think it was 1970-1975. Afterwards SGS should have adopted the standard naming for their IC line-up.

As already stated, contact me if you need those chips (H 257, H 258, H 202, H 203).

14 July 2022

Integrated circuits SGS "H 258 B1" and "H 257 B1"

One of the Nixie boards I bought in FN Ham Messe 2022 does not use the usual 7441 Nixie driver + 74xX Latch combo, but rather some undocumented SGS "H 258 B1" and "H 257 B1".

The pinout of H-258-B1 BCD(?)-to-Nixie driver is different from similar documented components (see http://madrona.ca/e/nixieref/index.html for a comprehensive description), so it is worth reversing it from this simple PCB.

I shot a picture of both sides of the board and created a single Xray-like view using an image manipulation software (The GIMP) as I've done in the past. This is the result and a zoomed view of one pair of these ICs:

Both sides of the board with SGS chips.
Both sides of the board with SGS chips.

SGS H257 and H258 combo.
SGS H257 and H258 combo.

The resulting pinout for H 258 B1 is:

1   input
2   input
3   input
4   digit 2
5   digit 3
6   digit 7
7   digit 6
8   GND
9   digit 4
10  digit 5
11  digit 1
12  digit 0
13  digit 8
14  digit 9
15  input
16  +V

I have no idea and no interest to discover which technology SGS used in 1974 for these parts. I will not use them in any of my projects because I would have no spares or direct replacements.

If you land here looking for a replacement, then contact me.

09 July 2022

Increase discharge current in XH-M239

The Lithium Battery True Capacity Tester Module XH-M239 discharges 18650 cells with a current of about 500 mA. It takes about 6 hours to test a single good cell: can we increase the discharge current?

The load is an 8 ohm 10W resistor while the current sensor is a 20 milliohm SMD resistor.

I quickly verified that if I parallel to the load a low-ohm power resistor the current increases and the mAh counter goes faster. So it should be possible to increase the drain on the battery under test and get a consistent result (with the error estimated in the previous post).

Would the circuit handle it? The tracks seem to be thick enough and we can easily measure their voltage drop, for example V across the battery vs V across the load. If we double the current to 1A, the 0.02 ohm sensing resistor would dissipate P = R * I * I = 0.02 * 1 * 1 = 0.02 W. 20 mW is well below the unknown rating of the resistor, which I would assume to be 250 mW.

Any resistor below 10 ohm with adequate power rating (10W or more) will do the trick if soldered in parallel to the stock load. For my quick test I went as low as 2.35 ohm load which resulted in a measured current of 1.5 A.

Note: you do it at your own risk as you understand BOTH stated AND not stated RISKS of this modification (short circuit, explosion, fire, skin burns, end of the World, end of Internet, human race extinction and so on).

Even Li-po cells from laptop battery packs should be able to withstand C to 2C discharge current so this trick is useful for testing a large amount of batteries with just one XM-M239 device.

04 July 2022

Li-Po capacity meter XH-M239: does it get it right?

In the last months I've used the FT-817 on the field and noticed that the Li-Po battery pack wasn't lasting as much as I expected. I had to choose: to build or not to build a device to measure the battery capacity? I opted for buying one and the choice was XH-M239 from aliexpress.

It tests one cell at a time with about 500 mA discharge current. It's slowish, but it mimics the consumption of a laptop I dare to say.

I set the stop voltage at 3,4 V because that's in the range for my intended use (3S "12V" pack) and all cells tested scored a very low rating! The best reached 1350 mAh, and many were below 500 mAh. None of them is brand new from a reputable source, so that was somewhat expected.

Nevertheless I started questioning XH-M239 readings. With a DVM, it's easy.

The measured battery voltage does match my DVM (that was checked against a reference voltage source).

The measured battery current does not match! See:

The real current is lower. Battery under test is connected to the screw-on terminals.
The real current is lower.
Battery under test is connected to the screw-on terminals.

The actual current flowing out of the battery is lower! The capacity is overestimated by 17%! As long as the time interval is correct. I will repeat the measurement at a higher battery voltage, in case we are hitting some sort of non-linearity. The measurement circuit uses a 0.020 ohm resistor and a "A53A" SOT-23-5 device, which is a voltage detector.

Alright. I don't need to guarantee the capacity of my battery packs, I simply want to build "good performers" with these second hand 18650 cells, so the higher mAh the better.