Tech Forum Questions

By using the resistance and capacitance values for the IC5A 556 timer IC we get one-shot periods between 0.5 and 1.6 seconds for the kHz switch position, and between 0.5 and 1.6 msec in the Hz position. The trimmers would adjust these to 1.00 sec and 1.00 msec respectively. I believe the switch labels (Hz and kHz) in the schematic diagram got swapped. The 1-sec period would let the counters count 0 to 999 pulses (0-1 kHz) and the 1 msec period would open the counters to count from 0 to 999 kHz (0-1 MHz). The calculations eliminate the possibility of IC1 as a prescaler or divide-by-x counter. Thus, IC1 probably is an obsolete CD4583. Don't give up hope: A CMOS Schmitt trigger CD4093 will do the same job, although it requires some rewiring. DigiKey has many in stock for under a dollar.

According to my ancient Motorola CMOS databook, MC14583B is a dual Schmitt trigger in a 16 pin package.  Channels A and B can be used independently or there is an exclusive OR output on pin 14. The outputs are tri-state with the control on pin 13. Pin 13 is not connected which is very, very bad practice. However, channel B input (pin 15) is tied high so only channel A is being used. Therefore, you can use any garden variety Schmitt trigger in its place.

The 4583 IC in your frequency counter is a non inverting dual Schmidt trigger. I found this in an old Motorola CMOS data book from 1991 #Q4/91 DL131 REV 3 on page 6-498. The Motorola part number is actually MC14583B. Only the A Schmidt is used in your circuit, the B Schmidt is unused. The Schmidt trigger is used in front of the counter IC1 to ensure a clean input to the counter. Typically the Schmidt trigger output will transition low when the input drops below 40% of the supply voltage and the output will go high when the input goes above 60% of the supply voltage. For the MC14583B device these thresholds are adjustable via external resistors through the positive, negative and common terminals. In your circuit those three pins 5, 6 and 7 are bussed together without a resistor and this sets the thresholds to around 40% and 60% of the supply voltage.

Pin 9 is the A input
Pin 4 is the A output
Pin 15 is the B input (unused so tied high to 9V)
Pin 10 is the B output (unused)
Pin 5 is the negative A (pins 5,6 & 7 are tied together to set the A device threshold)
Pin 6 is the positive A
Pin 7 is the common A
Pins 1, 2 and 3 are common, positive and negative for the B Schmidt (unused)
Pin 16 is VDD. Supply voltage, 18volt max for this device
Pin 8 is VSS. Supply voltage return.

A replacement for the '4583' could be the MC14093B or CD4093 available from Newark, etc., although these do not have adjustable thresholds they will be close to those of the 4583. These are quad two input NAND Schmidt triggers, so all unused input pins must be tied high (to 9V in your case).

I found an MC14583B IC in a 1991 Motorola Data Book. This part is a dual Schmidt trigger IC and appears to match the pinout  shown in the schematic. The pinout is not fully legible in the electronic issue. Using a Schmidt trigger in this application makes sense. I have attached a photo of the data sheet.

If IC1 is indeed an MC14583B or equivalent it should not be powered from 9V! The logic high output from Q1 is only 5V. The data sheet for the MC14583B indicates the minimum input voltage required to guarantee a logic high to be 80% of it's supply voltage. Also the logic high output voltage from IC1 is too high for the 5V downstream logic.

It is possible that IC1 is not actually defective but is not seeing a logic high due to poor design. This theory can be tested by substituting a 7 volt power supply for the battery. If it works at the lower voltage, I would modify the circuit to power IC1 from 5V.

I also question not having a resistor between the junction R1/C1 and the base of Q1 to limit input current to a non destructive level! This might best be accomplished by cutting a 1/16" gap in the track leading to the base of Q1 and soldering a 1K surface mount resistor across the gap.

Am attaching a ZIP file with 4 scanned pages of the MC14583B data sheet for your information. MC14583B.zip

The answer to question 11151 is it is an NE556 dual timer.

The chip you are looking for is a CMOS 4583. It is a dual adjustable  schmidtt  trigger. The 556 timer clocks the 4583 like a gate. I checked the usual places and it may be obsolete.

The best match for IC1 that I found is a Dual Schmitt Trigger, TC4583BP or NTE4583B.

Because most of the other ICs in this circuit are standard 4000-series CMOS parts, that indicates the 4583 at IC1 likely is also. Using that to refine the search, the part is a dual Schmitt trigger buffer.

The unique property of a Schmitt trigger gate is that it provides hysteresis.  When a slow-rising, slow-falling, or noisy analog signal is applied to an ordinary gate, that gate may oscillate and switch several times as the input crosses its switching threshold. But because this Schmitt trigger requires a much higher input voltage to switch high than it does to switch back low, it will clean up its analog input, and its output will switch only a single time.

In this circuit, that behavior is important because the input signal is being used as a clock for the counters.  Without the Schmitt trigger, some input signals might trigger multiple clock pulses per cycle, resulting in wildly incorrect frequency numbers.

Searching for Motorola's specific version number of this part, MC14583BCP, seems to produce better search results, revealing data sheets and even a seller of the part on Amazon!  However, because the circuit does not actually take advantage of the unique programmable hysteresis feature of the 4583 (by just tying pins 5, 6, and 7 together), any other CMOS Schmitt trigger should work just as well, if you can find something cheaper and don't mind slightly modifying the circuit.

This appears to be a dual Schmitt Trigger. I found the NTE4583B data sheet at: www.nteinc.com/specs/4500to4599/pdf/nte4583B.pdf VCC, GND placement is consistent with your Fig 1 schematic. Pin 9 is "A In" and Pin 4 is "A Out". So this would appear to be a Schmitt Trigger used to clean up the input signal.

The 4583, in that design, is an obsolete dual Schmidt trigger chip, which is intended to square up the input signal so it meets the minimum rise/fall time requirements of the downstream counter chips. Probably the simplest substitution would be a 4584 / 74C14 hex Schmidt trigger chip, with two of its inverters wired in series. The remaining four inverters should have their inputs grounded, to prevent excessive current consumption.

The chip you asked about the CD4583 is what is known as a Dual Schmitt Trigger ... that chip has been discontinued but some stores still have the NTE4583B which was their substitute for it. I have attached a .pdf file of the NTE Data Sheet for this chip. Worst case is you would need to rewire the schematic to use a more current version of an equivalent chip. nte4583B.pdf

One such store that says they have them is listed below:

www.moyerelectronics.com/BVModules/ProductTemplates/MoyerProductTemp/Product.aspx?productid=1e4bffa7-6961-4e1a-82f7-8a161ab401ea

Try looking at a MC14583B dual schmitt triger with only one side used. Pin out looks correct, Pin 9 is input and Pin 4 is output. Pins 5, 6, 7 are used to adjust hysteresis.

The 4583 is this part: www.nteinc.com/specs/4500to4599/pdf/nte4583B.pdf.

According to all my old data books, the 4583 IC is a Dual Schmitt Trigger, and NTE supplied them to the service industry, part number NTE4583. You can look at their data sheet here:
www.nteinc.com/specs/4500to4599/pdf/nte4583B.pdf

Supposedly, a company called "Mountain States Electronics has one in stock. Here is their address and contact info:
2107 South College Avenue
Fort Collins, CO 80526

Since the inventory for Mountain States showed only 1 in stock, here is another supplier of the TC4583 Schmitt Trigger chip. These people have a bunch of them and the price is definitely right:
http://store.americanmicrosemiconductor.com/tc4583bp.html

This is a common problem in any sensors that deal with moisture (soil moisture sensing or rain detectors or water level meters). Stainless steel probes may work better. I had better luck with non-metallic conductive probes. I use carbon rods from old carbon-zinc batteries. Carbon, most of the time does not react the way metals do and when it does, it does not cause non-conductive oxide layer like metals. If you can find conductive carbon rods, (I hope modern battery cells still have carbon rods) please try them out.

If the sensor is powered with a direct current voltage, you may be out of luck. However, here are some possible 'fixes'.

I read that the phone company, many years ago, had a problem with corrosion and switched from a negative ground to a positive ground, which helped to solve their corrosion problem. If you could insure the system is + grounded, this may help.

I think that most serious outside systems use AC sensors, and if they use DC, employ a positive ground, and are not powered unless a measurement is needed.

This is in response to the Fabian Hoffmann question about electron micrographs. We perform limited "community service imaging" of the type Fabian describes for school projects. We would need to know the scope of the project (usually just a few micrographs). Do let us know of your interest. www.marshall.edu/mbic/

Fritz, all you need is an appropriate 3-terminal voltage regulator to protect your Arduino boards. I don't know what voltage your board needs, so I suggest integrating an LM317T programmable regulator between the board's power jack and the board. The regulator will take the wall-wart's high voltage and reduce it to what the board requires. To program the regulator, connect it between the wall-wart and your board's DC input using this diagram as a guide:

Wiring isn't too critical (point-to-point), but keep lead lengths as short as practical. Be sure to include the 2 capacitors as they'll help "keep things stable" and prevent unwanted high-frequency oscillations. NOTE: the voltage rating of C2 should be above 24V as it's typically an electrolytic. Variable resistor R2 will let you dial in the output to what your board requires. BE AWARE: Keep the maximum current draw ** BELOW 1 AMP **, use a heat sink on the regulator (a TO-220 type clamp-on will be sufficient) and keep the regulator's input voltage BELOW 35 VDC!

If you don't want to bother with a variable resistor for R2, visit www.reuk.co.uk/LM317-Voltage-Calculator.htm as it has a nice table of standard resistor values to use for R1 and R2 for programming various output voltages (and other good info on the regulator).

According to the information about tne DG10A tube, it isn't a Nixie tube (which uses cold cathode shaped numbers that illuminate orange under a high voltage in the neon gas inside the tube), but a fluorescent glow tube, which uses a multi-segment cathode coated to glow green-blue under a high voltage, like the Nixie. This type of display was used in medium sized calculators and some digital clocks because the emitted light can be filtered, and a version with many digits using a multiplexed circuit was later used in calculators until the LED and LCD displays replaced them I still see calculators with these fluorescent displays. on many desks.

I found an eBay offer for the same type of tube (item #251596633619) that sells the tubes but has posted the wiring diagram for it. Look at the item diagrams to wire up the tube and test it.

The DG10A is not a nixie tube but is a 7 segment vacuum fluorescent tube. This vacuum fluorescent readout operates much in the fashion of a triode vacuum tube. A heated filament/cathode emits electrons that are attracted to any of the 7 anodes which are biased with a positive voltage. Each anode is coated with a material that fluoresces when the electrons strike the anode. Changing biasing on the control grid varies the intensity of the electron flow and therefore the brightness of the display. The filament requires about 50 milliamperes, which operates just below its incandescent level. About 0.8 VDC will provide the required current. Apply about 50 VDC to each anode (segment) that you want to turn on. For test purposes, the common control grid may also be biased at 50 VDC to provide maximum brightness. The pin-out for the DG10A may be found at www.radiomuseum.org/tubes/tube_dg10a.html

Attached is a zip file containing two files in response to Don Franklin’s question regarding a Quick Basic Program he wanted to develop. The code is “Very Well” documented with comments and should not require any additional explanation.

Listing_2.zip

'**************************************************************************
'*                     PROGRAM DESCRIPTION                               *
'**************************************************************************
'Program asks for the PATHNAME of the DATAFILE.
'   1.  The PATHNAME can have any name that conforms to the 8+3 character
'       limit of the earlier versions of DOS.
'   2.  The Default PATHNAME is "C:\QB\DATAFILE.TXT"
'   3.  The Datafile can have any number of Records but, they must conform                                                
'       to the following Spec.
'    
'       "mm/dd/yyyy", "nn, nn, nn, nn, nn, nn", "(nEVEN/nOdd)" cr-lf
'       | 12 chars |2 |      19 Chars        | 2|  14 Chars  |  2  |
'
'       for a total of 51 characters per record.
'
'The program opens the DATAFILE, determines how many records it contains
'   and loads them into an array of special TYPE "Records"
'While loading the data, the order of elements in the DATE are re-arranged
'       mm/dd/yyyy to yyyy/mm/dd
'
'The program then asks the user to input a 1, 2 or 3 as defined below.
'
'   (1) SORT IN ASCENDING ORDER: ALL ACTUAL NUMBERS DRAWN
'       (and the corresponding 'dates drawn')
'   (2) SORT IN ASCENDING ORDER: DATES DRAWN
'       (and the corresponding 'numbers drawn')+
'   (3) EXIT PROGRAM
'
'The program then prints 20 Data Records at a time waiting for the user
'   to hit any key to move on the the next screen.
'
' AllData()N = DATE DRAWN
' AllData()B = ACTUAL NUMBERS DRAWN
' AllData()C = RATIO OF EVEN/ODD NUMBERS CONTAINED
'
' Edited by Raymond Perry
' [email protected]
'**************************************************************************
'
'**************************************************************************
'*        DESCRIBE a MULTI DIMENSIONAL ARRAY TO HOLD THE DATA             *
'**************************************************************************
'
TYPE Records
    N AS STRING * 12
    Spcr1 AS STRING * 2
    B AS STRING * 19
    Spcr2 AS STRING * 2
    C AS STRING * 14
    CRLF AS STRING * 2
END TYPE
'
'**************************************************************************
'*        Designate the AllData() array to be re-dimensionable            *
'**************************************************************************
'
'$DYNAMIC AllData() AS Records
'
'**************************************************************************
'*               [DIMENSION other variables]                              *
'**************************************************************************
'
DEFINT A-Z
DIM IK AS STRING, TEMP  AS STRING
DIM Pathname AS STRING
'
'**************************************************************************
'*                     PROGRAM STARTS HERE                                *
'**************************************************************************
'
CLS
'
'**************************************************************************
'*                     PROGRAM STARTS HERE                                *
'**************************************************************************
'
'
'**************************************************************************
'*            Get the FileSpec of the File containing the DATA            *
'**************************************************************************
'
PRINT "Enter the complete PATHNAME of the file containing the data."
PRINT "EXAMPLE: C:\QB\DATAFILE.TXT"
INPUT Pathname
'
'**************************************************************************
'*            Use Default FileSpec if input is null                       *
'**************************************************************************
'
IF Pathname = "" THEN
    Pathname = "C:\qb\datafile.txt"
END IF
'
'**************************************************************************
'*            OPEN the File containing the DATA                           *
'*            BINARY access simplifies GETTING DATA                       *
'**************************************************************************
'
OPEN Pathname FOR BINARY AS #1
'
'**************************************************************************
'*            There are 51 characters in each record                      *
'*            There are K Records in the DATA FILE                        *
'**************************************************************************
'
K = LOF(1) / 51
'
'**************************************************************************
'*         REDIMENSION AllData() Array to make room for K elements.       *
'**************************************************************************
'
REDIM AllData(K) AS Records
'
'**************************************************************************
'*         GET the DATA RECORDS and hold them in the AllData(K) array     *
'*         Re-arrange the .N element to YYYY\MM\DD                        *
'**************************************************************************
'
FOR I = 1 TO K
    GET #1, , AllData(I)
    TEMP = CHR$(34) + MID$(AllData(I).N, 8, 4) + "/"
    AllData(I).N = TEMP + MID$(AllData(I).N, 2, 5) + CHR$(34)
NEXT
'
'**************************************************************************
'*         GET the User input to determine sort method or exit prog       *
'*         This is a "DO Forever" loop until the user enters "3" to exit  *
'**************************************************************************
'
DO
    CLS
    PRINT "Enter 1 to sort by NUMBER."
    PRINT "Enter 2 to sort by DATE."
    PRINT "Enter 3 to EXIT the program"
    IK = ""
    '**** Loop Here until user Enters 1, 2 or 3  **************************
    DO WHILE (IK <> "1") AND (IK <> "2") AND (IK <> "3")
        IK = ""
        IK = INKEY$
    LOOP
'
    IF IK = "3" THEN END
'
'**************************************************************************
'*         Continue if user entered a 1 or a 2                            *
'*         Swapping AllData(J) keeps all elements together                *
'**************************************************************************
'
    IF IK = "1" THEN ' SORT BASED ON NUMBERS DRAWN
        FOR I = 1 TO K - 1
            FOR J = 1 TO K - I
                IF AllData(J).B > AllData(J + 1).B THEN
                    SWAP AllData(J), AllData(J + 1)
                END IF
            NEXT J
        NEXT I
    ELSE        ' SORT BASED ON DATE
        FOR I = 1 TO K - 1
            FOR J = 1 TO K - I
                IF AllData(J).N > AllData(J + 1).N THEN
                    SWAP AllData(J), AllData(J + 1)
                END IF
            NEXT J
        NEXT I
    END IF
'
'**************************************************************************
'*         It is time to Print                                            *
'*         Swapping AllData(J) keeps all elements together                *
'**************************************************************************
'
' *********************[ TIME TO PRINT 20 lines ]**************************
    CLS
    FOR Z = 0 TO INT(K / 20) 'THIS CAUSES MULTIPLE PAGES TO PRINT
        FOR I = 1 TO 20  ' THIS LIMITS TO 20 ITEMS PER SCREEN
            IF (Z * 20 + I) <= K THEN
                Y = I + Z * 20
                PRINT Y, AllData(Y).N; AllData(Y).Spcr1; AllData(Y).B;
                PRINT AllData(Y).Spcr2; AllData(Y).C ' ALLDATA(Y).CRLF;
            ELSE
                EXIT FOR
            END IF
        NEXT I
' ***************[ BREAK AT 20 AND WAIT FOR ANY KEY ]************
        PRINT
        PRINT "PRESS ANY KEY TO PRINT THE NEXT SCREEN."
        IK$ = ""
        DO WHILE IK$ = ""
            IK$ = INKEY$
        LOOP
        CLS
    NEXT
LOOP
'
END

DATAFILE.TXT

"10/22/1994", "10,16,20,28,39,40", "(5Even/1Odd)"
"12/10/1994", "21,23,35,37,39,48", "(1Even/5Odd)"
"01/07/1995", "24,31,33,35,40,44", "(3Even/3Odd)"
"02/04/1995", "11,20,21,24,29,42", "(3Even/3Odd)"
"02/11/1995", "14,17,25,30,31,34", "(3Even/3Odd)"
"05/06/1995", "15,18,23,24,36,48", "(4Even/2Odd)"
"05/20/1995", "11,27,34,35,37,45", "(2Even/4Odd)"
"06/25/2003", "10,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2003", "18,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2003", "20,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2003", "10,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2003", "17,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2004", "11,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2004", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2004", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2004", "15,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2004", "17,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2005", "15,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2005", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2005", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2005", "14,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2005", "20,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2006", "15,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2006", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2007", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2007", "14,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2008", "20,24,26,28,41,44", "(4Even/2Odd)"
"10/22/1994", "10,16,20,28,39,40", "(5Even/1Odd)"
"12/10/1994", "21,23,35,37,39,48", "(1Even/5Odd)"
"01/07/1995", "24,31,33,35,40,44", "(3Even/3Odd)"
"02/04/1995", "11,20,21,24,29,42", "(3Even/3Odd)"
"02/11/1995", "14,17,25,30,31,34", "(3Even/3Odd)"
"05/06/1995", "15,18,23,24,36,48", "(4Even/2Odd)"
"05/20/1995", "11,27,34,35,37,45", "(2Even/4Odd)"
"06/25/2003", "10,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2003", "18,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2003", "20,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2003", "10,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2003", "17,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2004", "11,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2004", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2004", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2004", "15,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2004", "17,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2005", "15,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2005", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2005", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2005", "14,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2005", "20,24,26,28,41,44", "(4Even/2Odd)"
"06/25/2006", "15,16,31,35,38,43", "(3Even/3Odd)"
"06/28/2006", "12,19,26,34,46,47", "(4Even/2Odd)"
"07/02/2007", "24,25,26,36,37,47", "(3Even/3Odd)"
"07/16/2007", "14,16,22,24,26,37", "(5Even/1Odd)"
"08/23/2008", "20,24,26,28,41,44", "(4Even/2Odd)"

I don't have a quick answer for you, but the version of QuickBASIC you are using is quite out of date. Of the BASICs running on micros these days, I don't think any still use line numbers, REM statements and the like. The language is more structured with subroutine and function names. I too cut my teeth on HP educational BASIC from that era, but really don't miss RENUM as a edit feature. Now you compose programs in an editor and download them to a target. Our BASIC which targets various ARM processors can also be run on a PC in emulation mode, so you can start out writing programs there. www.coridium.us/files/setupBASIC.exe

Don, I'm not a QuickBASIC user, but what I see is you need matching SWAP statements (just like you say) in 290 & 347 when true, SWAP N$, SWAP B$, SWAP C$ then your arrays should stay in sync.

I'm not sure I follow your screen print requirement, however, the INPUT statement should allow you to both print an output and then wait for the Enter key to be pressed before continuing. Place the statement at the point you want to interupt. One more thing, the loop 330-339 will print the same value for D$ over and over, you want to move 311 to 331.

My suggestion would be to put an LM7812ACT linear three-pin regulator (about $0.69 each, plus shipping, from Digi-Key.com) between the solar panel and each fan. Be SURE to read the spec sheet carefully and use bypass capacitors on BOTH the input and output. (Guess how I know to warn about that!) You'll also need some sort of heat sink on each, though some scrap of aluminum should suffice -- my guess would be four square inches or more should do the trick. (If necessary, cut up an empty aluminum can, though fold the edges over to avoid sharp edge hazards.)

Using a "low dropout" regulator would mean more efficiency, but at a noticeably higher cost.

P.S.  I notice that you're in San Diego.  You can probably get the parts at Fry's Electronics, though for a little bit higher cost. The spec sheet can still be had at Digi-Key.com. (Wish Fry's would provide scooters for their mobility-limited customers!)

It’s not likely that the voltage from the solar collector, under load, will be enough to damage the fans. However, to be safe, you could put a 13 volt, 15 watt zener across the collector output. The fans will be drawing 1.53 amps while the collector is trying (best case) to put out 2.5 amps, so the zener will have to sink 0.97 amps. I could not find such a zener in the Mouser catalog, so the alternative is to use a power transistor amplifier, see diagram (the part numbers are Mouser).

The zener current is just the base current, about 33 mA. It is DO-41 (1 watt) and costs 22 cents. The transistor sinks 0.97 amps and dissipates 13 watts.  It costs 99 cents. A heat sink will be needed; Mouser part number 588-FA-T220-51E is suitable and costs $1.56. The heat sink is mounted vertical. It has two 0.091 solderable posts, diameter spaced one inch.

A good solution to this issue is to use a switching regulator. It has very high efficiency, close to 90%, and will take the 20+ VDC from your panel and even increase the current output some!! Go to "sul-tech" on YouTube, and you will find the solar optimizer schematic....hope it helps.

The 30W rating on your solar panel is very optimistic and requires a LOT of direct sunlight to reach that rating. You might need more than one panel to do what you want to do. I think you will find that you have the opposite problem of what you are concerned about. Solar panels have a very large output impedance, which means that the voltage will drop to a low value when you connect a load like an electric motor that has a low input impedance.

Also note that electric motors are rated at their RUNNING power requirements and they need much more current to START. You will need a buck-boost voltage regulator to do what you need to do. It raises the voltage when the light is dim and lowers the voltage when the light is bright.

Since your motors will require more than one amp you will need to find a regulator that is capable of supplying at least 2 amps and I recommend one rated at 3 amps or more.

Your solar panels only show that high of voltage when they are unloaded. Once you put the fans on them, the voltage will adjust to their rated voltage, providing you have enough sun light to drive them properly.

The other good news is that the fans will not burn up when more voltage is applied to them. They will run faster and wear out sooner, but to fry them, you would need much more than a single solar panel can produce.

The solar panel you have says 30 watts, but what they actually mean, is that under ideal conditions, it can produce 30 watts. Two panels would assure that the fan would run in less than ideal sun light.

I would use a simple LM7812 voltage regulator for each fan. The 7812 can take up to 18V in and as low as 5V and has a current rating of 1 amp. Based on your specs, you will only be drawing a little over half an amp on the 7.6 W fan and a little under a half amp on the smaller fans.  If you find that they get hot, you can easily add a heat sink.

I will also mention that I did something similar, running a boom box radio at the beach, and found that unless the panel is pointed at the sun constantly, the output will drift when fair weather clouds cross overhead. So, I connected 3 1000000 20V caps in series, which slowed down the drifting effect caused by clouds.

Another option is to use a solar charger controller like the one I picked up at harbor freight tools. You would hook up the solar panel to the controller, then the controller to the battery (car/marine), and run the fans off the battery. I would still use the LM7812 voltage regulator just to protect the fans.

I want to offer some facts that may help you form your own solution.

  1 - 7.4 volts happens to be 2X of 3.7 volts, and 3.7 volts happens to be the exact rating of most all cell phone batteries. Cell phone batteries can be bought very cheaply via the internet.

  2 - The next fact is that the battery door on Nikon cameras can be removed. Open it to approx 45 degrees and gently twist it out.

  3 - The next fact I would share is that a battery grip is a way to attach, usually two batteries, to the bottom of your camera. Some of the grips come with interval timers for timed exposures, they are all made in China, and as such, eBay is full of second party battery grips for many popular cameras. The grip might be the better way to modify your cameras without damaging them.

If you were to use cell phone batteries to make your own battery pack, your next challenge would be to build a charger for them, since charging them one by one would be labor intensive. Making a battery pack of the cell batteries would require them to all be the same rated capacity. Connect them in series, in pairs, to bring them up to 7.4 volts and parallel as many as you like to increase capacity to meet your requirements.

Lastly, NEVER attempt to open a battery, especially a Lithium battery. If you were to expose the Lithium to air, it most likely will explode and seriously injure you or result in your death.