I have this old 10MHz Velleman HPS10 handheld oscilloscope. Its really handy for working on vehicle sensors, CAN bus fault finding, as well as on the bench.

Its a little awkward to use (hence the sellotaped crib sheet) but is rugged and portable, and does the job.

However, I have a couple of dislikes, which really need fixing:

1. It has 5 AA Nimh batteries, for portable use, and can be charged in situ using a 9v supply. However, the batteries dont last very long in field use. I would like to upgrade the scope to be Lithium powered.

2. With the scope soft powered off, it still drains the batteries. So when you reach out for it after a month or so, the batteries are flat. No good for me, or for the batteries.

The standby off drain current is rather high at0.5mA, which explains the discharged state after a month. On duracell alkaline batts it should give 20hrs use. I barely get half an hour on my used Nimh batteries, and they are costly to replace.

I want a hard power off switch when its put into storage. The soft power button is stll handy as it retains your scope settings, whilst hard power is the same as a reset of the device.

I know, 10+ years on and I finally get around to making these mods! As the scope has surpassed its expected life time, lets give it some extended battery life.

Lets get to work!

Supplies

Toggle power switch/button

2 Nokia mobile phone batteries BL4YW. These can be bought for a few quid each on ebay. Or free for good recycled batteries.

Male female dc plug connectors x2
Dremel
Hot glue gun

Step 1: Design

I intend to power the scope with 2 nokia bl4yw batteries in series. These will be removeble and charged externally individually using a tp4056 charger. See my other project on recycling mobile phone batteries for more details.

The 5 AA battery compartment needs to make space for 2 x nokia BL4YW batteries. Its a tight squeeze so some dremel action will be required.

On a 2000mah battery pack and drain of 300mA, I should get 7+ hours of use.

A toggle on off switch will be mounted on the side, in series with the 2 batteries.

I will piggyback the switched lithium supply to the 9v DC input connector. The 9v dc socket will be blocked off to prevent the batteries from directly being charged. The scope has an onboard linear regulator stepping down to 5v.

Note that I avoided using a single lithium battery with a buck regulator, as the high frequency switching noise would interfere with the scope. Hence opting for two batteries in series making 8.4v.

You could insert a 2S charge protection board, if space permits, but I prefer the option of being able to swap out the batteries. As I have rather alot of these BL4YW's batteries. Also I want to avoid having to buy another dedicated 2S 8.6v lithium regulated power supply. Also some of my used batteries do not charge up to the full 4.2v, but that's not an issue for this application.

Step 2: Make Space!

I removed the battery compartment spring connectors and had to dremel to make some space for the batteries.

Drill 2 holes for the power switch wires as my toggle switch is surface mounted.

Step 3: Solder and Hot Glue

Solder up the batteries in series with the toggle switch and piggyback it to the 9v dc input connector.

Hot glue the toggle switch, to secure and and insulate it.

Step 4: Reassemble and Charge

Guide the lithium battery terminal connectors to the battery compartment, ensuring everything is insulated, especially the lithium battery connections.

Block off the 9v dc connector with either hot glue or pvc tape.

Close up the case. Disvonnect and Charge up the batteries externally, reconnect and power up.

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Step 5: Use It !

i also knocked up some handy crocodile and probe leads using cctv bnc connectors, for low voltage use.

I kept one of toggle switch terminals bare (on the switched output) so you can self probe the battery voltage. This helps to monitor voltage as I do not use a battery protection board for under voltage cutoff..

I started with a pair of "used" fully charged batts at 8v. I left it powered on and the battery voltage dropped to 7.1v. (loaded) after 8 hours of use. As lithiums dont take kindly to being disxharged under 3.5v each, I would recharge at 7v to maintain good battery life. That's much better than the half hour on my used NiMh batteries. I do like the ability to self probe the battery voltage, so cool!

These scopes now sell on ebay used, for more than what i paid new (£80 from Maplins). Now, if only it had a backlight like its elder brother the HPS40. Stop right there !