Analogue Design - Recent Threads

RE: 9V NiMH charging

ariajames_121 — Sat, 15 Mar 2025 20:01:33 GMT

It’s great that you found a true 9V replacement with 7-cell NiMH batteries since older 6-cell versions always had voltage issues. For charging, a proper circuit with delta-V detection and a safety timer would be ideal. You could consider designing a custom circuit using an MCU with a constant current source and termination detection. If you want a simpler approach, a low-current linear regulator with a series resistor can work, but it may not be as efficient or safe in the long run. Have you looked into smart chargers like the La Crosse or Opus models?

9V NiMH charging

koudelad — Wed, 02 Oct 2024 17:12:15 GMT

Hello,

9V batteries have always been a pain for me... Expensive, low capacity, almost every DMM / tester needed them.

I just bought a 9V NiMH battery: https://www.westinghousebattery.com/Ni-MH-Rechargeable/Premium-Series.html . To my surprise, it is not made from 6 smaller cells (which would give ca. 7.2-8.4 V), but 7, which has nominal voltage of 8.4, but when charged, can have almost 10 V. This makes it a true primary 9V battery replacement. I am not sure when these became available, but I remember older 6-cell "9 V" NiMH that were kind of useless, because all appliances thought the battery is discharged, due to the lower nominal voltage.

However, I never really had a charger for this kind of battery. I have heard that cheap chargers only use 12 V DC power supply with in series resistor in series to limit the current to ca 30 mA.

Do you have any suggestion for a charging circuit? I am open to building something, even using an MCU. I would love it to have a small small charging current (20-30 mA) or slightly higher (50 mA), a safety timer and the delta V detection. There is a famous old MAX713 charger, but according to the features, it offers C/4 to 4C charging and C/16 trickle charging, which is too high. Most commercially available hobby chargers also have a minimum current of 100 mA.

Thank you,

David

RE: 9V NiMH charging

shabaz — Fri, 11 Oct 2024 09:12:08 GMT

Yes, it would be greatly simplified with a microcontroller.

I'll document the rest somewhere and maybe finish it if it helps anyone.

I couldn't settle on a target microcontroller (and didn't fancy coding anything currently), so I figured I may as well make it microcontroller-agnostic, i.e., one could unpopulate those additions if the microcontroller interface is used.

It's just a mental exercise, I have no serious suggestion for anyone to construct this unless they enjoy soldering a lot of parts. Plus, my design decisions won't be the same as others; I just used what parts I was familiar with (I'd already tested that constant-current portion in that Bluetooth project, so I lifted that as-is).

RE: 9V NiMH charging

koudelad — Fri, 11 Oct 2024 07:41:51 GMT

Thank you, but to be honest, I think a single 8-bit 6-pin MCU would replace the timing circuit and maybe also the charging logic.

RE: 9V NiMH charging

shabaz — Fri, 11 Oct 2024 00:36:13 GMT

It was bugging me that there wasn't a timeout. I've been in the position where I've forgotten to unplug a charger.

The timer needs to be somewhere in the region of 16-24 hours. The design below (untested) uses a load of divider chips. It looks a lot, but 74HC4060 are cheap (and probably there's no size restriction). All parts here shouldn't cost more than a few $ total.

The crystal output is just divided loads, and when 19 hours is reached, the TIMER_EXPIRY signal goes high, and that also prevents any more counting.

The timer isn't essential, and if there's a microcontroller attached, then it's redundant (unless such a hardware timer is preferred).

The main circuit is tweaked to add the TIMER_EXPIRY connection as an input:

Also, while I was at it, I replaced the constant current resistor with a rotary selector, since it appears there are PP3 batteries with a range of capacity. Probably overkill to have such granularity, but the rotary switch could be replaced with a wire link to permanently set a current if desired.

RE: 9V NiMH charging

dougw — Sat, 05 Oct 2024 00:16:27 GMT

Cool idea, but I'm wondering if it would tend to try to overcharge, as it tries to maintain a constant current?

RE: 9V NiMH charging

koudelad — Fri, 04 Oct 2024 17:54:03 GMT

Interesting, thank you for the inspiration.

RE: 9V NiMH charging

scottiebabe — Fri, 04 Oct 2024 17:44:26 GMT

I use a USB-C PD module, diode, resistor, and ohms law FTW.

If you want to make your own PCB you could consider an switching LED driver and design around a 5V USB input.

One random example:

ww1.microchip.com/.../mic2287c.pdf

RE: 9V NiMH charging

genebren — Fri, 04 Oct 2024 15:51:20 GMT

Very Nice! This is something that I would like to look into further in the future. I really do appreciate your efforts to assist and to promote a true sense of community here on element14!

RE: 9V NiMH charging

shabaz — Fri, 04 Oct 2024 01:50:31 GMT

I had some time, to lay out the PCB. This board is 100 x 60 mm and several different PP3 battery holders will fit. All parts are jellybean. The optional microcontroller is connected to the row of pin-headers on the left side of the photo (without it, the user would need to disconnect after 24 hours as mentioned above).

This is the schematic:

I'll wait a day in case anyone spots any errors/major problems, and then I'll generate the Gerber files and place the project on GitHub. There's no guarantee it will work, but if anyone tries the circuit, please report back with any feedback/mods!

RE: 9V NiMH charging

battlecoder — Thu, 03 Oct 2024 20:57:08 GMT

I haven't tried this myself but after Googling some more, here's a project using an Arduino: www.hackster.io/.../intelligent-charger-for-9v-nimh-rechargeable-batteries-v1-61cbd6

RE: 9V NiMH charging

shabaz — Thu, 03 Oct 2024 20:07:42 GMT

I think the circuit below would do it. It's based off of a simpler charger here: Smart Doorbell System – Part 6 – Chime Module Complete Circuit Design and based on information from a battery mnfr PDF doc which specifies that it should be OK to charge at 0.1C for at least a day.

This circuit charges at 20 mA, and would take 15 hours to fully charge the battery. The battery would need to be manually disconnected within 24 hours.

However, there is also a microcontroller interface, so that you could turn it on/off based on a timer if desired (or any other logic circuit that can perform the timing).

Without the microcontroller, you'd need to remember to disconnect after a day of charging. If you need a PCB for this, let me know (it's fairly easy for me to convert to a PCB, since I've already created the schematic in the same CAD software that would create the PCB).

There's no guarantee that it will work, but it would be easy to test and then that would provide reasonable confidence with it (I'd trust this more than a cheap charger).

RE: 9V NiMH charging

koudelad — Wed, 02 Oct 2024 19:40:01 GMT

I think this is safe here, below is an extract from the datasheet:

I think no more than 1.35 V per cell is expected.

RE: 9V NiMH charging

battlecoder — Wed, 02 Oct 2024 17:56:23 GMT

This would be a very interesting project. I quickly googled some designs and they are all very simple and relatively high current compared to what you are looking for. I'm more familiar with Li-Ion charging that I am with NiMH, so I wouldn't know where to start designing a circuit other than looking at charging curves and a breakdown of the charging process, then figuring out how to monitor and control voltage/current with a microcontroller before putting something together.

RE: 9V NiMH charging

shabaz — Wed, 02 Oct 2024 17:55:08 GMT

Hi,

A normal alkaline PP3 (advised for DMMs etc unless they specify otherwise) usually have a voltage of 9.6V or so when fresh, depleting from there. Using a 10.5V battery might be risky, since that's almost a volt higher.

RE: Nice new AD Parts

DAB — Thu, 14 Mar 2024 18:24:01 GMT

Interesting list of products.

Analog Devices has always had a lot of very useful products.

Nice new AD Parts

michaelkellett — Wed, 13 Mar 2024 16:12:17 GMT

I was going to post this in the Analogue Forum - but there isn't one, or maybe Audio (nope), or even "Instrumentation " - no.

So it has to be a blog here.

Just had a note from ADI about a few rather neat parts:

ADA4510-2 Op Amp with DigiTrim[emoticon:7d377b609b6f44bf9290e3d8a0b9a733]
Analog Devices' ADA4510-2 precision, 40 V, ±70 nV/°C, rail-to-rail input and output op amp features DigiTrim

A very nice low noise, low offset dual op amp remarkably similar to the TO OPA2192.

Currently only available in 8 pin SOIC.

ADL5960 Analyzer Front End

Analog Devices' ADL5960 10 MHz to 20 GHz integrated vector network analyzer front end supports various LO interface configurations

It looks interesting but of course it isn't a complete VNA - I don't know enough about the design of such things to tell if its would make a good VNA or just a cheapish one.

The chip is £133 and the eval board is about £800.

ADG6412/ADG2412 Switches

Analog Devices' ADG6412 and ADG2412 0.5 Ω RON quad SPST switches provide high continuous current carrying capability

These are nice (if pricey at £6.94 each) quad SPST solid state switches capable of switching serious current and a wide voltage range.

and finally the:

MAX17614 Ideal Diodes/Power Source Selector Device

Analog Devices' MAX17614 4.5 V to 60 V, 3 A, ideal diode and power source selector has current limit, UV, and OV protection

These look quit nice - I rather wish I had fitted them to my laser controller - it has four buck regulators capable of about 20W each but no easy way to current limit them. If I'd known about these parts I could have used them both for isolation and protection.

RE: Nice new AD Parts

cstanton — Thu, 14 Mar 2024 13:08:03 GMT

Done!

RE: Nice new AD Parts

michaelkellett — Thu, 14 Mar 2024 12:46:26 GMT

Yes please - nice to be the first post !

RE: Nice new AD Parts

shabaz — Thu, 14 Mar 2024 12:10:57 GMT

Same here, it's a nice-to-have but in the back of my mind for if/when the need arises.

The time cost adds up too! Bit of a learning curve with tools/software too, that can chew up days : ( I purchased a new logic analyzer recently, need to learn that (hoping it won't take as long, I tried out the software before purchasing).

RE: Nice new AD Parts

cstanton — Thu, 14 Mar 2024 11:31:03 GMT

Analogue Design - would you like me to convert and move this post over?

RE: Nice new AD Parts

michaelkellett — Thu, 14 Mar 2024 09:41:32 GMT

I took a quick look at the VNWA - looks very interesting.

But I must resist rushing out to buy one since I have about a dozen Rabbits on the go right now. (Rabbits are side jobs without paying customers.)

RE: Nice new AD Parts

michaelkellett — Thu, 14 Mar 2024 09:27:22 GMT

Thanks Chris,

Extending Embedded and Microcontrollers by the addition of Analogue Design would work fine for me.

It has sub fora of Embedded, DSP and PIC Microcontrollers so adding an Analogue Design forum to that set would be reasonable.

Designing complete embedded systems almost always involves some analogue, if only in the power supply si it makes some sense to bundle them together.

RE: Nice new AD Parts

cstanton — Wed, 13 Mar 2024 19:34:16 GMT

"Is there a way to get a list of ALL the existing fora ?"

Almost all groups have a forum, someone in their infinite wisdom when we moved to Verint, decided to name all of the forum applications "Forum", so you have to go by the group name.

"But ideally I wanted an Analogue Design forum - or close to that - the point of the post is to inform people who do chip level analogue design, rather than have a passion for ADI themselves."

Okay, I'm happy to create a dedicated forum for that, but hmm, you may be onto something that there might not be a good fit somewhere for it at the moment? I had a look through Technologies and there are the groups listed on /sitemap - maybe renaming 'embedded' or another group to something close to suitable could accommodate a forum dedicated to this?

RE: Nice new AD Parts

shabaz — Wed, 13 Mar 2024 19:26:12 GMT

Hi Michael,

Great selection! I saw that ADL5960 chip recently, and I couldn't tell if it would be good or not, the dev-board outputs two IF signals in analog form, and to extract the performance would either need more processing in the analog/frequency domain (e.g. down-convert to zero IF) and then LPF and then sample it, or would need to be sampled at the IF and then process it, to get the gain and phase magnitudes. The software to control/measure/compute would be a lot of work, but there is open source (e.g. LibreVNA PC application) that could perhaps be a base from which to start. Also, there's no frequency generation on the eval board, so that would be needed (for both the measurement frequency sweep and for the LO). The chip/dev-board could be a very attractive way to create an embedded VNA for scientific instruments or a more general instrument could be made with a couple of the boards for 2-port. Unfortunately, the 10 MHz limitation is because a key part of the circuit is fully integrated into the chip, which is an excellent thing for size and performance at high frequencies but doesn't scale to the lower frequencies.

MiniCircuits released (a couple of years ago) a VNA based on their parts, as a sort of 'training' VNA, but it was very expensive, $10k or so). It would be nice if AD could find a way to offer something ready-made much like the ADALM-PLUTO, at a lower cost, perhaps deliberately reduced to 3 GHz, so that it doesn't eat into sales of their 20 GHz product at the full price.

The affordable option that's tempted me for a while is VNWA 3EC (£259+tax), which has the main problem that it only supports up to 1.3 GHz, but other than that, the specs are good, and the PC software is quite functional although the menu structure is very unintuitive. The VNWA has the advantage of working from 1 kHz upwards! Dynamic range is good (not excellent) and reduces into VHF and beyond, but at that price, it's a completely usable 2-port VNA. And, because it's been around for ages, most bugs are ironed out, so there'd be little doubt at the measurements it provides. One quite interesting feature is that it's possible to extend the impedance range (into milliohm and up to 100s of kohm) using a neat add-on circuit called RF-IV, turning the system into a really good general impedance meter. I've built that circuit for a DIY 'N2PK' VNA (which only works to 60 MHz, so that's quite a restriction), but that RF-IV circuit functions to a GHz or so apparently, and is compatible with the VNWA. I *think* the circuit is patented, which is why there's no commercial product (other than high-end Keysight instruments) that offers it, but fortunately, it was easy to DIY. The N2PK VNA has an extremely good dynamic range (better than some commercial VNAs), so for impedance measurements from 50 kHz to 60 MHz, it's exceptionally good. Hopefully VNWA would be good too.

Really impressive specs on those ADG switches! The MAX chip looks nice too. A while back I was looking at using TI LM5050 chips, which are cheaper but need external MOSFETs, for OR'ing a couple of supplies, but in the end that particular requirement went away.