Let there be light – anytime, anywhere.
Clive’s Corner by Clive Bagshaw
A feature of MicroNews, Clive’s Corner is a place created for the sharing of knowledge, tricks, and tools. The Corner is where you read about clever microscopical hacks - and submit your own. Clive’s Corner is the namesake of SFMS member Clive Bagshaw, who has spent a lifetime looking into microscopes - including 50 years studying protein reactions.
This is installment #6 of Clive’s Corner - perhaps the most ‘enlightening’ CC yet!
A few months ago, I was invited to participate at an outdoor event to introduce the world of plankton as seen under a microscope. The organizers said they had some power extension cables but not all the tables would be within reach of electricity. No problem from my cheap Amscope SE305 stereo microscope, which is battery powered and is recharged by a USB cable, but this option is not available for most compound scopes. That got me thinking about adding a battery supply to my Amscope 120 and Swift 350 compound microscopes.
Removing the four screws from the plate under the Amscope 120 microscope revealed there was plenty of room to add a battery (Figure 1a). The 110/240 v AC supplied a Switching Power Supply Transformer whose output voltage was controlled by a potentiometer wheel to give up to 3.1 V that fed into the light source, a 1 W light emitting diode (LED). My Swift 350 microscope had similar components with a slightly different arrangement, so it was modified with the same procedure. A suitable battery for powering the LED is a 3.7 V 1200 mAh rechargeable Li-ion which comes with its own USB recharging cable linked via a JST connector (Figure 1b).
Figure 1a. Existing LED power supply in the base of an Amscope 120 microscope. The lead in the bottom right attaches to the LED light source via its JST connector.
Figure 1b. Rechargeable 3.7 V battery with USB plug attached via 2-pin JST connectors.
Figure 1c. Underside of microscope showing the addition of battery, switches, variable resistor, and output coaxial plug.
Figure 1d. Top: the existing light intensity control wheel and added slider switch. Bottom: Battery power potentiometer knob and a push button switch with coaxial output connector.
The first step was to drill holes in the microscope base to add a slider switch and potentiometer for light intensity adjustment. That was no problem for me as I had already drilled and threaded a half dozen other holes in the body to mount various accessories. However, this is an unlikely route that owners of research-grade microscopes would be willing to take. In any event, many of these use filament lamps that are power hungry and could not be supported by a small battery. I will come back to this audience later. While I had the drill in hand, I also added holes for a push button switch and output coaxial connector so that the battery supply was available to power external light sources, such as an LED flashlight for fluorescence excitation (a forthcoming CC topic). A component list, with embedded web links, is given below. In addition, electrical wire and a soldering iron are required to complete the modifications. Some of these individual components cost less than $1 but, in these cases, are supplied in packs of 5 or more. So, a bonus is that you will have spares for more DIY projects.
Component List
100 Ohm potentiometer and knob
Optional extras
To add battery power to the microscope, it is necessary to cut the existing back and red wires to the LED light source and insert a 2-pole slider switch (Figure 1d top) via a terminal strip connector. This allows switching between the original AC driven supply and the battery source. The battery source is connected via a 100 Ohm potentiometer (variable resistor) to control the LED intensity (any value potentiometer between 100 and 500 Ohm will work). A fixed 1 Ohm resistor was added in series to the 100 Ohm variable resistor as a precaution to prevent the slightly higher voltage (3.7 V) from overdriving the LED. The value of this resistor depends on the limiting resistance of the potentiometer when on its minimum setting. With an appropriate fixed resistor in place, the maximum light intensity when using battery power will be similar to that when plugged into an AC source. The two-pin JST wire connector of the battery was incorporated into the circuit so that the battery could be recharged in situ from the supplied USB connector (Figure 1b) and was accessible from a hole in the bottom plate. This dedicated USB connector has a standard 5 V input and a 3.7 V output to charge the Li-ion battery. An additional option, not required for standard operation, is a second circuit connected across the battery to a coaxial socket via a push button switch to supply 3.7 V output for other accessories.
Figure 2. Diagram showing existing LED power supply (upper circuit) with added components for battery-powered operation (lower right) connected by the slider switch.
The microscope LED was specified as 1 Watt which, at 3.1 Volt input, indicates a maximum current of 0.32 Amps (Watts = Amps * Volts). I calculated a current closer to 0.18 Amps (0.18 V measured across the 1 Ohm resistor; Ohms = Volts/Amps)), so the LED is underpowered, which extends its working life. Nevertheless, there is sufficient light for brightfield and darkfield illumination using a patch stop. The Li-ion battery had a rating of 1200 mAh (= 1.2 Amp hours) so it should power the microscope for around 6 hours. For more extended use, a USB portable supply designed for phone charging, could be connected via the USB charging connector. A 10 Ah device should last for more than 50 hours, which should be plenty for field trips.
Figure 3. Free-standing microscope using battery power.
Having battery power on your microscope is not only useful for outdoor demonstrations and research work in the field, but it also means that in the event of a power outage, you can continue to use your microscope at home (Figure 3). For those of you who cannot bring themselves to drill holes and cut wires in their microscope, an alternative solution is to buy a portable power inverter with 110 V AC outlet. But this will add 3 pounds weight to your gear.
To view a video demonstrating these installation procedures in detail, as applied to a Swift 350 microscope, click here.
PS. If you need a 1 Ohm resistor, let me know. I have 98 left in the pack!